Allow creating projects in non-empty folders with a confirmation popup

[aaronfranke]

Follow-up to godotengine/godot#15835, the linked PR replaces godotengine/godot#39220.

Describe the project you are working on: New ones.

Describe the problem or limitation you are having in your project:

Creating projects in non-empty folders can be a dangerous operation, but is sometimes desired, especially by @SubSage. The specific use case here is that if you create an empty repository on GitHub, then clone to your computer, the cloned repo contains a .git folder, so you can't create a project there, and have to perform the workaround at the bottom of this proposal.

Describe the feature / enhancement and how it helps to overcome the problem or limitation:

The enhancement is to allow creating projects in non-empty folders with a warning and a confirmation popup, rather than prevent users from doing this completely.

Describe how your proposal will work, with code, pseudocode, mockups, and/or diagrams:

Branch: https://github.com/aaronfranke/godot/tree/project-in-non-empty

PR: godotengine/godot#42526

The PR changes the message from an error to a warning, and adds a confirmation dialog that looks like the below (I moved the windows so that you can see everything at once, but normally they appear on top of each other).

If this enhancement will not be used often, can it be worked around with a few lines of script?:

It can be worked around by creating the project elsewhere, then closing Godot, then copying the files to the desired location, then opening Godot and browsing to the new location.

Is there a reason why this should be core and not an add-on in the asset library?:

This is about the project manager, so it can't be an add-on in the asset library.

[Zireael07]

Just dropping by to say that Sage isn't the only one who would like this 😉