Object.get_meta & has_meta doc mentions is_valid_identifier but deprecated (prefer is_valid_ascii_identifier)

**Your Godot version:**

4.6

**Issue description:**

The doc for `Object.get_meta` and `has_meta` says:

> Note: A metadata's name must be a valid identifier as per [StringName.is_valid_identifier()](https://docs.godotengine.org/en/4.6/classes/class_stringname.html#class-stringname-method-is-valid-identifier) method.

But clicking on the hyperlinks shows that `is_valid_identifier` is deprecated:

> Deprecated: Use [is_valid_ascii_identifier()](https://docs.godotengine.org/en/4.6/classes/class_stringname.html#class-stringname-method-is-valid-ascii-identifier) instead.

So we might as well just mention `is_valid_ascii_identifier()` from the start.

**URL to the documentation page:**

https://docs.godotengine.org/en/4.6/classes/class_object.html#class-object-method-get-meta
https://docs.godotengine.org/en/4.6/classes/class_object.html#class-object-method-has-meta