CBA_fnc_addBISEventHandler

[commy2]

This adds CBA_fnc_addBISEventHandler

Was brought up in the ACE public slack. You can never pass arguments to event handlers and you can't retrieve the id for removing it from inside either.

This PR follows the idea of the recently added _thisScript (script handle passed as variable) to spawn (https://community.bistudio.com/wiki/spawn)

Using CBA_fnc_addBISEventHandler adds these variables to the executed function:

• _this - default event handler information
• _thisType - type of the event (e.g. Fired, Draw3D, keyDown)
• _thisId - id used to remove the event (e.g. via ctrlRemoveEventHandler)
• _thisArgs - additional arguments passed when the event handler was added
• _thisFnc - CODE, a copy of the function

It can be used on objects, dialogs and controls, as well as add mission event handlers (using missionNamespace as "target")

Examples:

• A one time reloaded event handler (prints "bananas" once after first reload):

[player, "reloaded", {
    systemChat _thisArgs;
    player removeEventHandler [_thisType, _thisID];
}, "bananas"] call CBA_fnc_addBISEventHandler;

• Print text once after 300 frames:

[missionNamespace, "EachFrame", { 
    if (diag_frameno < _thisArgs) exitWith {};
    systemChat "hello world"; 
    removeMissionEventHandler [_thisType, _thisID]; 
}, diag_frameno + 300] call CBA_fnc_addBISEventHandler;