[feature] "Built-in" Override for SDL to instead use SDL12-compat for SDL enabled titles.

Feature Request

I confirm:

• that I haven't found another request for this feature.
• that I have checked whether there are updates for my system available that
  contain this feature already.

Description

SDL1.2-compat should be a "built in" override for SDL1.2 games within Proton, and included as a replacement DLL similar to the use of FAudio or DXVK as drop-in replacements for similar windows libraries respectively.

Justification [optional]

The reason why this should be included in Proton is because this addresses the issue of Steam Deck/Steam Input support for older games that utilize that API for controller support on Windows, so that proper (emulated) Xbox Controller inputs are passed in-game. Examples of Steam games with similar controller issues through Proton for controller support, that has their issues addressed through SDL1.2-compat being used as a replacement are "Cave Story+", and "Star Wars Jedi Knight: Jedi Academy", and proton directly performing that override would automate the fixes going forward.

Risks [optional]

One risk that should be noted is the potential for SDL1.2-compat to not properly support the older game due to bugs or unaddressed behavior. In this event, 'native" overrides rather than "built-in" may be more acceptible for those particular applications, to use the version of SDL1.2 shipped with the game.

References [optional]

No source files or tests are named. Start by examining how Proton integrates FAudio and DXVK as replacement components, then determine where SDL1.2-compat could be included and selected for SDL1.2 titles. Done means eligible titles use SDL1.2-compat automatically while retaining a native override for games with compatibility problems.