[Open Assets] Redberries 2

All major features included with Redberries have been merged into the SRB2 Classic fork: https://srb2classic.net/ so you'll want to keep an eye on that if you like custom builds with new features. Redberries in turn will be entering a stable, maintenance and bugfix only state.

Changelog:

• Updated codebase for parity with Reveries
• Added new quit messages to fit the style and width of the new quit prompt
• Some internal optimisations
• Fixed horizon line rendering in OpenGL
  • thanks to a fix from ChromaticPipe
• Fixed compiling on GCC 15
• Fixed compiling on cmake and clang
  • thanks to multiple fixes from Hanicef
• Fixed some MRCE menu things crashing the game
  • thanks to a fix from Lugent

• Fixed crash when opening the sound menu... again
• Replaced the auto-assign shield ability button thing with instructions attached to mapping the Shield button
  • This was way too easy to press on accident and mess up your controls
• Removed some Reveries leftovers
  • Shield is now only referred to as Shield Ability and not as Peelout
  • PeeloutSpecial hook renamed to ShieldButtonSpecial
    • This change will be added to Reveries later
  • Fixed super forms being able to use some shield abilities
• ShieldButtonSpecial no longer fires if Spin and Shield are mapped to the same button