Fix ClassDB API portability with some android and editor classes

- `EditorNavigationMeshGenerator` was being registered as part of the Core API,
even after d3f48f88bb. We must make sure to
set Editor as the current ClassDB API type before creating an instance.

- The `VisualScriptEngineSingleton.constant` property has a property hint string
that's different between tools and non-tools builds. This commit makes the
hint string to no longer be set in `_bind_methods`, and to instead set it in
`_validate_property`. This way it's ignored when calculating the API hash.

- `JavaClassWrapper` is now registered in ClassDB on all platforms,
using a dummy implementation on platforms other than Android.
This fixes API portability between Android and other platforms.

- Updated `--class-db-json` command to ignore non-virtual methods that start
with an underscore (see: 4be87c6016).

modules/mono/csharp_script.cpp

@@ -106,7 +106,7 @@ Error CSharpLanguage::execute_file(const String &p_path) {
 void CSharpLanguage::init() {
 
 #ifdef DEBUG_METHODS_ENABLED
-	if (OS::get_singleton()->get_cmdline_args().find("--class_db_to_json")) {
+	if (OS::get_singleton()->get_cmdline_args().find("--class-db-json")) {
 		class_db_api_to_json("user://class_db_api.json", ClassDB::API_CORE);
 #ifdef TOOLS_ENABLED
 		class_db_api_to_json("user://class_db_api_editor.json", ClassDB::API_EDITOR);