Ability to change user data path in Project Settings

[Calinou]

I think it makes sense to be able to change the user data path (where user:// points to) in the Project Settings, ideally per-OS.

Something like:

• Windows User Data Path
• Linux User Data Path
• OS X User Data Path
• Android User Data Path

[bojidar-bg]

👍 Even better, move this to export settings.

[Calinou]

👍 Even better, move this to export settings.

User data is also read and written when running from the editor, so those settings should probably be in the Project Settings.

[bojidar-bg]

@Calinou ~ I mean export.cfg, since this is per-platform, and shouldn't really be in project settings....

[akien-mga]

Superseded by #13236 which has implementation details (sorry, forgot to look for this one before writing it :)).