Docs: Update Control class to properly reflect behavior of Themes on Control Children

[tetrapod00]

Supersedes https://github.com/godotengine/godot/pull/90289. Apologies if this kind of salvage is frowned upon in the main repo; I've been doing this to clear the backlog in the docs repo recently.

Closes https://github.com/godotengine/godot/issues/88534.

The wording "as long as a chain of [Control]s is uninterrupted" is copied from the Theme docs.

I made some additional changes:

• Don't call theme items "parameters" - I believe either "items" or "properties" is correct here.
• Don't mention that you can override the theme with the inspector, since this is implicit from the fact that this is a class with a theme property.
• Link to the [member theme].

[Mickeon]

The documentation is sometimes torn on what to call these. Sometimes it's "theme items" and sometimes it's "theme properties". I think the former is more common.

[Repiteo]

Thanks!