Rewrite NtUserSetCursorIconData

Rewrite of NtUserSetCursorIconData
Fixes:

• Memory leaks
• Cursors left in an unpredictable / unhealthy state, including pointers to freed memory, when an operation failed
• Decision whether a cursor uses an ACON or CURSOR as the underlying structure based on user provided flags, instead of cursor flags, which were not even set in the first place.
• Allowing a usermode caller to corrupt the cusor structure, by converting an ACON with a smaller allocation size into a CURSOR