Disallow creating a project in the Home or Documents folder

[clayjohn]

This is a temporary fix for #74678.

This PR does 2 things:

1. It disallows creating projects in the "Home" or "Documents" folders which are the default paths used by the editor for new projects. Users will have to select another path, or create a new folder. The previous warning is still in place for other non-empty folders

Project creation menu by default

Project creation menu when another non-empty path is chosen

2. It removes the option to delete the project contents. This option is useful, but without further safeguards it is much to dangerous. We need to remove it ASAP until we can implement it in a safer way. I left the previous code commented out so that we are incentivized to fix it.
   

[Calinou]

I suggest also preventing creating projects directly within OS.get_executable_path(), as per #60332. This way, #60332 will be fully addressed and you won't be able to "brick" the editor by creating a project anymore.

[clayjohn]

OS.get_executable_path()

Added!

[akien-mga]

Thanks!

[Calinou]

PS: While this is labeled cherrypick:4.0, it's probably a good idea to create a dedicated 3.x PR for 3.6 too (the project manager code is different, so this can't be cherry-picked cleanly).

[YuriSizov]

Cherry-picked for 4.0.1.

[skyatgit]

Will the option to delete project content come back in the future?

[AThousandShips]

As the PR says it's temporary and while working on a way to do it safely, see also #56420