L4D2VR 2.0.1 - mirrored left hand, trigger-release throws, one-hand aim on short guns (test build)

Test build on top of 2.0.0 (OpenXR-only; see the 2.0.0 notes for the Proton/launch requirements). Untested in game; please report how it feels.

• Left hand mirrored: a gun, melee weapon or item in your left hand is now held by a mirrored left hand. The arms come from the correct shoulders and the sights stay on the aim line (ItemHandMirror).
• Throwing:
  • Hold the trigger of the hand with the grenade, swing, and let go. Every release throws immediately. A slow release lobs or drops it.
  • Velocity is your hand's release velocity x1.5.
  • The held grenade is rolled upright (ThrowableHoldAngleOffsetDeg, default 0,0,20).
• Short guns (pistol, magnum, Uzi, silenced SMG, MP5) aim from the trigger hand only. The support hand still helps with recoil (VrHandsTwoHandedAimShortGunsRearHandOnly). Rifles and shotguns stay two-handed.
• Installer 1.1.1: finds the system certificate bundle on any Linux distribution, and creates the Monado route's Proton prefix folder.