Slimmed down variant from the reverted #8375.
The rationale behind the name change is to give Godot's project file a unique
extension (".godot") that can be registered on the OS to be associated with
the Godot binary (OS registration not implemented here).
This PR also adds the possibility to start the game or editor if launched
with the project.godot passed as argument, which paves the way for allowing
a similar behaviour on a double-click in the OS file manager (code originally
by @Hinsbart).
Closes#6915.
I can show you the code
Pretty, with proper whitespace
Tell me, coder, now when did
You last write readable code?
I can open your eyes
Make you see your bad indent
Force you to respect the style
The core devs agreed upon
A whole new world
A new fantastic code format
A de facto standard
With some sugar
Enforced with clang-format
A whole new world
A dazzling style we all dreamed of
And when we read it through
It's crystal clear
That now we're in a whole new world of code
The other subfolders of tools/ had already been moved to either
editor/, misc/ or thirdparty/, so the hiding the editor code that
deep was no longer meaningful.
