Fix #4135: Keep bool-to-int conditional in its local

Once comp(x != 0) is removed for a bool x, `int n = b ? 1 : 0` becomes a
plain copy of the bool, and copy propagation replaced every load of n with
`(b ? 1 : 0)`. Refuse copies between bool and non-bool variables rather
than requiring identical types, which would also block legitimate copies
such as dynamic -> object or Derived[] -> Base[].

ICSharpCode.Decompiler/IL/Transforms/CopyPropagation.cs

@@ -124,6 +124,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 					{
 						return false; // non-local code move might change semantics when there's split variables
 					}
+					if (v.Type.IsKnownType(KnownTypeCode.Boolean) != target.Type.IsKnownType(KnownTypeCode.Boolean))
+					{
+						return false;
+					}
 					switch (v.Kind)
 					{
 						case VariableKind.Parameter: