Add fine-grained disabling of SourceGenerators

This allows manual testing and/or alternate source generators to
provide functionality without conflict.

modules/mono/editor/Godot.NET.Sdk/Godot.SourceGenerators/ScriptSerializationGenerator.cs

@@ -16,7 +16,7 @@ namespace Godot.SourceGenerators
 
         public void Execute(GeneratorExecutionContext context)
         {
-            if (context.AreGodotSourceGeneratorsDisabled())
+            if (context.IsGodotSourceGeneratorDisabled("ScriptSerialization"))
                 return;
 
             INamedTypeSymbol[] godotClasses = context