Remove vtable method class prefix with --disable-name-namespacing

Fix for #2438

Author: Supreeeme

bindgen-tests/tests/expectations/tests/vtable_no_namespacing.rs

@@ -0,0 +1,4 @@
+// bindgen-flags: --disable-name-namespacing
+struct Interface {
+	virtual void Method() = 0;
+};

bindgen-tests/tests/headers/vtable_no_namespacing.hpp

@@ -1137,8 +1137,10 @@ impl<'a> CodeGenerator for Vtable<'a> {
                         _ => panic!("Function signature type mismatch"),
                     };
 
-                    // FIXME: Is there a canonical name without the class prepended?
-                    let function_name = function_item.canonical_name(ctx);
+                    let mut function_name = function_item.canonical_name(ctx);
+                    if ctx.options().disable_name_namespacing {
+                        function_name = function_name.rsplit_once('_').unwrap().1.to_string();
+                    }
 
                     // FIXME: Need to account for overloading with times_seen (separately from regular function path).
                     let function_name = ctx.rust_ident(function_name);