docs: document default values for Filters properties in XML docs

Continues the work started for #5917 (already covered Targets, Layouts,
LayoutRenderers and Target Wrappers), extending the same pattern to the
NLog.Filters namespace so default values show up in IntelliSense and the
generated API docs.

Adds a regression test that scans all settable NLog.Filters properties
against the generated XML documentation file and fails if any of them is
missing a documented default value.

src/NLog/Filters/ConditionBasedFilter.cs

@@ -50,6 +50,7 @@ namespace NLog.Filters
         /// <summary>
         /// Gets or sets the condition expression.
         /// </summary>
+        /// <remarks><b>[Required]</b> Default: <see langword="null"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public ConditionExpression Condition { get; set; } = ConditionLiteralExpression.Null;
 

src/NLog/Filters/Filter.cs

@@ -53,6 +53,7 @@ namespace NLog.Filters
         /// <summary>
         /// Gets or sets the action to be taken when filter matches.
         /// </summary>
+        /// <remarks>Default: <see cref="FilterResult.Neutral"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public FilterResult Action { get; set; }
 

src/NLog/Filters/LayoutBasedFilter.cs

@@ -51,6 +51,7 @@ namespace NLog.Filters
         /// Gets or sets the layout to be used to filter log messages.
         /// </summary>
         /// <value>The layout.</value>
+        /// <remarks><b>[Required]</b> Default: <see cref="Layout.Empty"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public Layout Layout { get; set; } = Layout.Empty;
     }

src/NLog/Filters/WhenContainsFilter.cs

@@ -45,12 +45,14 @@ namespace NLog.Filters
         /// <summary>
         /// Gets or sets a value indicating whether to ignore case when comparing strings.
         /// </summary>
+        /// <remarks>Default: <see langword="false"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public bool IgnoreCase { get; set; }
 
         /// <summary>
         /// Gets or sets the substring to be matched.
         /// </summary>
+        /// <remarks><b>[Required]</b> Default: <see cref="string.Empty"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public string Substring { get; set; } = string.Empty;
 

src/NLog/Filters/WhenEqualFilter.cs

@@ -45,12 +45,14 @@ namespace NLog.Filters
         /// <summary>
         /// Gets or sets a value indicating whether to ignore case when comparing strings.
         /// </summary>
+        /// <remarks>Default: <see langword="false"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public bool IgnoreCase { get; set; }
 
         /// <summary>
         /// Gets or sets a string to compare the layout to.
         /// </summary>
+        /// <remarks>Default: <see cref="string.Empty"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public string CompareTo { get; set; } = string.Empty;
 

src/NLog/Filters/WhenNotContainsFilter.cs

@@ -45,12 +45,14 @@ namespace NLog.Filters
         /// <summary>
         /// Gets or sets the substring to be matched.
         /// </summary>
+        /// <remarks><b>[Required]</b> Default: <see cref="string.Empty"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public string Substring { get; set; } = string.Empty;
 
         /// <summary>
         /// Gets or sets a value indicating whether to ignore case when comparing strings.
         /// </summary>
+        /// <remarks>Default: <see langword="false"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public bool IgnoreCase { get; set; }
 

src/NLog/Filters/WhenNotEqualFilter.cs

@@ -52,12 +52,14 @@ namespace NLog.Filters
         /// <summary>
         /// Gets or sets a string to compare the layout to.
         /// </summary>
+        /// <remarks>Default: <see cref="string.Empty"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public string CompareTo { get; set; } = string.Empty;
 
         /// <summary>
         /// Gets or sets a value indicating whether to ignore case when comparing strings.
         /// </summary>
+        /// <remarks>Default: <see langword="false"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public bool IgnoreCase { get; set; }
 

src/NLog/Filters/WhenRepeatedFilter.cs

@@ -54,12 +54,14 @@ namespace NLog.Filters
         /// <summary>
         /// How long before a filter expires, and logging is accepted again
         /// </summary>
+        /// <remarks>Default: <c>10</c></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public int TimeoutSeconds { get; set; } = 10;
 
         /// <summary>
         /// Max length of filter values, will truncate if above limit
         /// </summary>
+        /// <remarks>Default: <c>1000</c></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public int MaxLength { get; set; } = 1000;
 
@@ -67,30 +69,35 @@ namespace NLog.Filters
         /// Applies the configured action to the initial logevent that starts the timeout period.
         /// Used to configure that it should ignore all events until timeout.
         /// </summary>
+        /// <remarks>Default: <see langword="false"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public bool IncludeFirst { get; set; }
 
         /// <summary>
         /// Max number of unique filter values to expect simultaneously
         /// </summary>
+        /// <remarks>Default: <c>50000</c></remarks>
         /// <docgen category='Filtering Options' order='100' />
         public int MaxFilterCacheSize { get; set; } = 50000;
 
         /// <summary>
         /// Default number of unique filter values to expect, will automatically increase if needed
         /// </summary>
+        /// <remarks>Default: <c>1000</c></remarks>
         /// <docgen category='Filtering Options' order='100' />
         public int DefaultFilterCacheSize { get; set; } = 1000;
 
         /// <summary>
         /// Insert FilterCount value into <see cref="LogEventInfo.Properties"/> when an event is no longer filtered
         /// </summary>
+        /// <remarks>Default: <see cref="string.Empty"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public string FilterCountPropertyName { get; set; } = string.Empty;
 
         /// <summary>
         /// Append FilterCount to the <see cref="LogEventInfo.Message"/> when an event is no longer filtered
         /// </summary>
+        /// <remarks>Default: <see cref="string.Empty"/></remarks>
         /// <docgen category='Filtering Options' order='10' />
         public string FilterCountMessageAppendFormat { get; set; } = string.Empty;
 
@@ -106,6 +113,7 @@ namespace NLog.Filters
         /// <summary>
         /// Default buffer size for the internal buffers
         /// </summary>
+        /// <remarks>Default: <c>1000</c></remarks>
         /// <docgen category='Filtering Options' order='100' />
         public int OptimizeBufferDefaultLength { get; set; } = 1000;