Better respect auto-translation of static strings

[KoBeWi]

I noticed that GUI nodes make heavy use of RTR. It has 2 problems:

• minor one is that this makes the strings translated in scene nodes (mostly affects FileDialog)
• major one is that it forces the string to be translated even if auto_translate is disabled

I changed RTR to TTRC where internal auto-translation can be used (Buttons and PopupMenus; since #75012 it works even in the editor). For dynamic strings I added a new ATR() function, which is the same as already existing atr(), but it's used for strings that should be fetched for translation.

Partially addresses #80549 If we make auto_translate propagated, this PR is required to make it actually work.

Note that we need to add ATR to the translation fetch list (I think it's done on the translation repo?)

[KoBeWi]

I just noticed that NOTIFICATION_TRANSLATION_CHANGED is not handled by most nodes, so changing locale at runtime won't update them if they use ATR(). I guess it's something for another PR.

[akien-mga]

Superseded by #86222.