move "Tab size" to the "Project setting" and create "Default tab size" for the "Editor setting"

[Sergwest585]

I believe that I am not the only one who opens other people's projects for contributions. Often, the tab size (as well as the choice between tab and space) differs from project to project.
Why not set the tab size on the project settings side, and add a default tab size on the engine settings side, which will set the tab size for each newly created project?

[arkology]

There is PR to allow per-project override of editor settings. I think it will be enough.