screen-cast: Increase size of maximum mouse pointer bitmap

Currently, the maximum size for a mouse pointer bitmap for screen casting is 64x64 pixels. However, this limit is hit way too often as it is way too low and results in crashes in either gnome-remote-desktop or mutter. For example: The a11y settings in g-c-c allow setting a larger pointer bitmap in order to increase the visibility of the mouse pointer. With the current limit of 64x64 pixels it is not possible to use the larger variants of the default mouse pointer bitmap, without experiencing any crash. Another way to hit the limit is when display scaling is used or some game uses a custom (large) mouse pointer bitmap.

The VNC backend in gnome-remote-desktop does not seem to have a maximum pointer bitmap size. The RDP backend on the other hand has a maximum pointer bitmap size at 384x384.

Use this size (384x384) as maximum size instead of the current 64x64 size for mouse pointer bitmaps to avoid crashes in mutter and gnome-remote-desktop and to ensure that bigger mouse pointer bitmaps can be used.

Should be merged together with: gnome-remote-desktop!17 (merged)