Allow user to import old bevy projects

[Freyja-moth]

What problem does this solve or what need does it fill?

Many users will already have existing projects that they might want to use the editor with. Currently the only way to do so it by creating a new project in the editor and manually copying the code from the old project.

What solution would you like?

Allow users to import an existing project to use the editor.

What alternative(s) have you considered?

Keep it as is, but this will increase friction to editor adoption which isn't ideal