[WIP] Feature pointerlock

[Yanrishatum]

Resolves #568
Implements API allowing for locking mouse for relative free movement and locking mouse inside game boundaries.

There are currently unresolved questions regarding implementation pending. See here #568 (comment)

Todo:

• JS: lock/unlockPointer.
  • Should pass movement when mouse was unlocked by user?
  • Should ignore click that relocks mouse?
• JS: windowLock. Should be implemented at all?
• SDL: lock/unlockPointer. Automatic unlocking when game loose focus is handled by SDL.
• SDL: windowLock. Need to expose SDL api.
• DirectX: lock/unlockPointer.
• DirectX: windowLock.
• Flash: Reimplmenet lock/unlockPointer. Should be implemented?
• Flash: windowLock. Should be implemented?
• General: windowLock naming convention?

Edit 26/05/20: Dropping flash/DX in favor of having it at least for JS/SDL. Also dropping windowLock.

[Yanrishatum]

I'm closing this PR, as I'm working on a slightly different re-implementation of it, which will require changes to hlsdl/hldx (HLSDL is already fully functioning, but HLDX still needs some work with cursor capture). When ready, new PR will introduce:

• SDL, DirectX and JS pointer lock (i.e. hide cursor, suppress EMouseMove and delegate relative mouse movement to the callback.
• SDL and DirectX window lock (i.e. trapping the cursor within window client area. Not possible on JS. For SDL and DX, pointer lock also implies window lock.
• Not in Heaps API, but accessible via SDL/DX: Moving the cursor on the screen. Both relative to the window and in screen-space.

[ncannasse]

Nice :)