Only try to do EOS operations on a path if there's actually a Wineprefix there

[CommandMC]

Previously, trying to enable/disable/check the status of the EOS overlay for a game with an invalid prefix directory would lead to an error message.
We're now handling this correctly (not enabling/disabling it, always reporting that it's disabled)

Technically, this works by adding:

• a new type, ValidWinePrefix. It's an extension of the Path type, meaning it already makes sure the string inside it is a valid path, and it now also verifies that there's a user.reg file inside the directory it's pointing to
• a new function inside the EOS handler, getWinePrefixFolder. It deduplicates some of the logic used in the enable/disable/isEnabled, and now also makes sure the configured prefix path is contains a valid prefix

Error message before:

No error message now:

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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)

[flavioislima]

Nice fix!