Move localized number formatting methods to TranslationServer

[timothyqiu]

Closes #96105. The idea is salvaged from it.

This PR transfers format_number(), parse_number(), and precent_sign() from TextServer to TranslationServer.

• The new methods don't have default parameters. The locale / language should be explicitly specified.
  • A "global" language does not make sense in most places since different translation domains can be showing different languages.
• The methods on TextServer and TextServerExtension are deprecated, but still kept for compatibility.

Godot should look exactly the same after this change. Most work to explicitly specify the language has been done in #110378.

[bruvzg]

There's nothing text server specific to these methods, and TextServerAdvance implementation is not using ICU (since we are not compiling localization part of it, which is handling similar stuff), so TranslationServer is indeed a better place for these.

[Mickeon]

Well, this is going to be mildly annoying for localization, ironically. The descriptions between the old and new methods are so similar, if it weren't for the language-to-locale change, so this will inevitably create more translation strings.
Consider duplicating the description to the deprecated methods to ease the burden at least.

[timothyqiu]

I added a description of the behavior when language is empty to the TextServer{,Extension} version's descriptions. This is the primary difference between the old and new versions.