Caused by what looks like slight differences between how AOT treats an empty array (vs JIT builds) when it marshals the array (AOT sends a null pointer, JIT sends a pointer to an empty array)
This was causing issues in both builds (AOT crashed immediately because of the null pointer, JIT read from out-of-bounds memory)
-Also allows cropping the edit window when the size doesn't fit (e.g using 4x4 near the bottom of the screen can result in a 4x2 edit window, etc.)
-Fixed a display issue when the number of edited columns & rows didn't match
Prevent queueing another update while the previous update is still running, which should prevent most issues.
Also slightly improves performance for the SNES tilemap viewer (which was causing the freeze when displaying an 8bpp 1024x1024 tilemap)
Notes:
-Uses a copy of VirtualizingStackPanel (to include fixes done after preview6) + fix another issue in lists
-Fixes memory leaks when closing windows (by setting DataContext to null, etc.)
