Exposing more project settings for documentation

[AThousandShips]

For project settings to be available for documentation, more importantly for doctool and ci to work, they have to be defined before this line:

godot/main/main.cpp

Line 2525 in d8e242c

doc.generate(doc_base);

Moved a number of settings from below this to project_settings.cpp, could also move them inside main.cpp but felt this was a better place to put them, can also move other settings out of main but left ones not causing this problem to keep the changes minimal

Documented a few of the settings that I had a clear idea of what they did and how to explain.

[AThousandShips]

I think the settings should be in a proper order now

[YuriSizov]

Couple of suggestions for the descriptions themselves, but LGTM otherwise.

[AThousandShips]

Went ahead and updated the documentation in SceneTree as well as some descriptions were taken straight from there.

[AThousandShips]

Identified a few more settings, editor related all of them, that still are inaccessible to documentation, will investigate if I can expose them.

[AThousandShips]

Went through and it looks like all settings in the ProjectSettings menu are now documented or possible to document, that was one tedious slog

If someone else wants to entertain themselves by looking if settings are exposed you can simply add something like "EMPTY" to the descriptions of all properties in ProjectSettings, which makes it stick out if its unexposed, then it will just say the usual "no desc" or something.

[YuriSizov]

Thanks!

[AThousandShips]

Thank you!

[YuriSizov]

Cherry-picked for 4.0.2.