CoordGeom: Improve const correctness.

Also mark constant as float when it makes sense.
Subpic interfaces: Improve the const correctness.

The ABI isn't modified but the interfaces are for internal use anyway.
SubPicImpl: Minor cosmetics.
DX7 Subpic: Avoid resetting the static subpicture when possible.

Also use safer locking.
DX9 Subpic: Avoid resetting the static subpic and the subpic pool when possible.

Also use safer locking.
DX9 Subpic: Remove unused code.
Memory subpic: Mark some global variables static and minor cosmetics.
SubPicAllocators: Const correctness and minor cosmetics.
Subpic queues: Cosmetics.

Be less aggressive when invalidating the queue without threading while at it.
SubPic provider: Minor cosmetics.
Subtitle queue: Clearer display of the queue stats.

Show the start and end time of the queue without trying to normalize with current time.