C#: Assume 64-bit types when type has no meta

When the C# bindings generator finds a type without meta assume the type
refers to the 64-bit version of the type:
- `float` is converted to `double`
- `int` is converted to `long`

modules/mono/editor/Godot.NET.Sdk/Godot.SourceGenerators.Sample/ScriptBoilerplate.cs

@@ -7,7 +7,7 @@ namespace Godot.SourceGenerators.Sample
         private NodePath _nodePath;
         private int _velocity;
 
-        public override void _Process(float delta)
+        public override void _Process(double delta)
         {
             _ = delta;