Generate valid C# when a field with an anon type starts with '$'

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

src/Generator/Generators/CSharp/CSharpSources.cs

@@ -64,7 +64,9 @@ namespace CppSharp.Generators.CSharp
             if (id.All(char.IsLetterOrDigit))
                 return ReservedKeywords.Contains(id) ? "@" + id : id;
 
-            return new string(id.Select(c => char.IsLetterOrDigit(c) ? c : '_').ToArray());
+            return new string((from c in id
+                               where c != '$'
+                               select char.IsLetterOrDigit(c) ? c : '_').ToArray());
         }
 
         #endregion

src/Generator/Passes/RenamePass.cs

@@ -363,7 +363,7 @@ namespace CppSharp.Passes
 
             var sb = new StringBuilder(decl.Name);
             // check if it's been renamed to avoid a keyword
-            if (sb[0] == '@')
+            if (sb[0] == '@' || sb[0] == '$')
                 sb.Remove(0, 1);
 
             RemoveUnderscores(sb);

tests/CSharp/AnonTypes.h

@@ -147,6 +147,9 @@ extern "C" {
                                         example_lib_kref_com_plangrid_example_Request_Response_ErrorResponse(*ErrorResponse)(example_lib_kref_kotlin_Error error);
                                         example_lib_kref_kotlin_Error(*get_error)(example_lib_kref_com_plangrid_example_Request_Response_ErrorResponse thiz);
                                     } ErrorResponse;
+                                    struct {
+                                      int i;
+                                    } $serializer;
                                 } Response;
                             } Request;
                         } example;