Merge Linux and Deck Branches

[dotaxis]

I've finally got this to a point where the Linux branch should no longer be necessary.

I need some more people to test it before I can merge, but I figured I would get this started now.

Changes:

• Use 7th Heaven EXE installer and allow it to handle the .NET dependencies (much faster!)
• Rework prefix rebuild - wipe prefix and use Steam to build a Proton 7 prefix from scratch (should fix blank box in text bug)
• Remove reliance on Protontricks (speed!)
• Only install custom controller mapping and SteamDeckAutoConfig mod if SteamOS is detected
• Detect install paths of Proton 7, SRL2 and FF7 by reading libraryfolders.vdf
• Support non-standard SteamLibrary locations using STEAM_COMPAT_MOUNTS (experimental)
• Refactored to improve speed and stability

With these changes the same script can be ran on a Linux desktop or a Deck, and Deck-specific tweaks won't be applied on a desktop. Linux functionality only tested on Arch so far.

[dotaxis]

Updated dev branch to use Proton 8 again. I want to see if we're still getting bad load times now that Proton 8.0-5 is out.

[dotaxis]

Proton 8 still has the bug. :(

Rolled back to Proton 7 again.