Check prefix folder is correct before deleting it

[arielj]

This PR adds a few checks before deleting the prefix of a game to check that we don't delete the wrong thing:

• if the path is the same as the game installation path, we don't delete it (would delete all games)
• if the path is the same as the default/shared prefix path, we don't delete it (would delete all prefixes)
• if the path does NOT contain a drive_c folder, we don't delete it (it's either not a prefix or there's something off in it)

I also used the opportunity to move some code into a new utils/uninstaller.ts file to make main.ts a bit smaller.

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Use the following Checklist if you have changed something on the Backend or Frontend:

• Tested the feature and it's working on a current and clean install.
• Tested the main App features and they are still working on a current and clean install. (Login, Install, Play, Uninstall, Move games, etc.)
• Created / Updated Tests (If necessary)
• Created / Updated documentation (If necessary)

[CommandMC]

Note that Proton prefixes (not using umu) will never have this folder. Maybe we also want to check for a pfx folder?