Fix #3702: Don't rewrite GetValueOrDefault() to == true in ?. chains

Turning bool?.GetValueOrDefault() into `== true` ends an enclosing
null-conditional chain, so `c?.Flag.GetValueOrDefault()` became
`(c?.Flag == true)` of type bool instead of bool?. A following `?? false`
then fails to compile (CS0019), and a following `.ToString()` yields
"False" instead of null when c is null. Keep the call when its target is
part of a ?. chain.

ICSharpCode.Decompiler.Tests/TestCases/Correctness/NullPropagation.cs

@@ -7,6 +7,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Correctness
 		static void Main()
 		{
 			new NullPropagation().TestNotCoalescing();
+			new NullPropagation().TestNullableBoolInChain();
 #if CS72
 			new NullPropagation().TestRefStructNotCoalescing();
 #endif
@@ -15,6 +16,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Correctness
 		class MyClass
 		{
 			public string Text;
+			public bool? Flag;
 		}
 
 		void TestNotCoalescing()
@@ -29,6 +31,26 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Correctness
 			return c != null ? c.Text : "Hello";
 		}
 
+		void TestNullableBoolInChain()
+		{
+			Console.WriteLine("TestNullableBoolInChain:");
+			foreach (MyClass c in new[] { null, new MyClass(), new MyClass { Flag = false }, new MyClass { Flag = true } })
+			{
+				Console.WriteLine(EqualsTrue(c));
+				Console.WriteLine(GetValueOrDefaultToString(c) ?? "<null>");
+			}
+		}
+
+		bool EqualsTrue(MyClass c)
+		{
+			return c?.Flag == true;
+		}
+
+		string GetValueOrDefaultToString(MyClass c)
+		{
+			return c?.Flag.GetValueOrDefault().ToString();
+		}
+
 #if CS72
 		ref struct ByRefLikeStruct
 		{

ICSharpCode.Decompiler.Tests/TestCases/Pretty/NullPropagation.cs

@@ -32,6 +32,7 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			public readonly MyStruct ReadonlyStructField;
 			public string Text;
 			public MyClass Field;
+			public bool? NullableBool;
 			public MyClass Property { get; set; }
 			public MyClass this[int index] => null;
 			public MyClass Method(int arg)
@@ -380,5 +381,15 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return x?.ToString();
 #endif
 		}
+
+		private static bool Issue3702(MyClass c)
+		{
+			return c?.NullableBool.GetValueOrDefault() ?? false;
+		}
+
+		private static string Issue3702ToString(MyClass c)
+		{
+			return c?.NullableBool.GetValueOrDefault().ToString();
+		}
 	}
 }