Expose Player Ability Functions to Lua

Part of a series of isolations from !1472 (closed). Exposes P_DoFiring, P_DoSpinAbility, P_PlayerShieldThink, and P_DoJumpStuff to Lua. P_DoFiring handles Ringslinger abilities, P_DoSpinAbility handles spin-button abilities, P_PlayerShieldThink handles shield abilities, and P_DoJumpStuff handles jump-button abilities. Useful if you want to call a certain ability's behavior without actually using it. A use case would be calling P_DoJumpStuff in an JumpSpinSpecial hook to allow a character to have two CA_ abilities. Or calling P_PlayerShieldThink when pressing custom 1 to allow a character to still use shield abilities when jump or spin have abilities in the air already.