[WIP] Add pseudolocalization support to Godot

[angad-k]

GSoC Pseudolocalization project

This is a work in progress PR
This PR will be updated over the course of the next two months as I implement the pseudolocalization feature in Godot for GSoC'21. The GSoC project link for this can be found here and the original proposal can be found here. Also check out the todo list here. Demo project for this feature can be found here. PR for Godot-Docs tutorial can be found here. PR for Godot-Demo-Projects can be found here.

[Calinou]

I tested this pull request locally. Here's how it looks like when debugging pseudolocalization is enabled:

It seems to be working well so far 🙂

[Calinou]

Documentation changes:

[akien-mga]

Looks pretty good, I left some comments on style and a few possible improvements.

Once ready, the commits should be squashed before merge, so that we have a clean Git history once merged. This can be done with an interactive rebase.

Might be worth doing it in a new branch and new PR if we want to preserve the development history in this PR (so the new PR would supersede this one). The squashed version would also be easy to backport to the 3.x branch with git cherry-pick -x <commit> and then solving merge conflicts.

[akien-mga]

You can add a pseudolocalization_enabled property with ADD_PROPERTY additionally to the setter and getter. This will remove the setter and getter from the docs and expose the property instead, which is more user-friendly.

For its documentation, you can copy what you had in the setter, and edit it to start following our style for boolean property descriptions: If [code]true[/code], .... (No need to say what happens if false since nothing happens.)

[akien-mga]

Instead of this here, you can use EDITOR_DEF_RST where you actually use it in TranslationServer directly. The _RST part will also enable restart if changed. (See my other comment about caching the value too.)

[angad-k]

Squashed the commits and added PR #51395