chore/export workflow

[nyarw]

adds .github/workflows/export.yml, it builds and exports the game when a tag is pushed and uploads them to a draft release.

• verifies the tag matches config/version in project.godot
• verifies the .NET sdk version in Rhythia.csproj matches .github/godot_version.txt
• tags containing - (for example v0.2.0-rc1) are created as prereleases and are exported as debug
• builds an Inno setup installer and uploads it

other stuff:

• deleted prefabs/modifier_button.tscn, it was a stale scene referencing a missing script, caused errors
• reverted the Renderers array fallback in Runner.cs
• made the export paths in export_presets.cfg proper, and added the macOS bundle identifier

todo:

• installer/rhythia.iss, the script needed for inno to build the installer
• automatic release notes