Add pseudolocalization demo

[angad-k]

Demo project PR for the pseudolocalization feature I'm adding to Godot as part of GSoC.

[Calinou]

This demo should be submitted on the 4.0-dev branch instead of master, as the master branch should only contain demos compatible with the latest stable Godot release (3.3.2 as of writing).

If pseudolocalization is ever backported to a 3.x release, we can backport the demo in the future as well.

[akien-mga]

This demo should be submitted on the 4.0-dev branch instead of master

Fixed.

[aaronfranke]

Thanks! For the record, this was added to Godot 4.0 in godotengine/godot#51395