Update mouse cursor shape after changes

[Sauermann]

resolves #45936
supersedes #58913

This fixes some cases where the mouse cursor shape did not change automatically, but instead required a MouseMove to update.

#58913 introduced a bug that caused a recursive call loop (#58960) for AnimationTimelineEdit and AnimationTrackEditTypeAudio, both of which change the default cursor shape on every mouse move event:

InputEventMouseMove -> set_default_cursor_shape() -> update_mouse_cursor_shape() -> InputEventMouseMove -> loop back

This patch makes sure that the recursion loop is broken in Control::set_default_cursor_shape(), which is a prudent safeguard.
I verified, that I can not reproduce #58960 with this patch.

A different alternative to resolve the recursive loop would be to not use set_default_cursor_shape during every mouse move in AnimationTimelineEdit::gui_input and AnimationTrackEditTypeAudio::gui_input.
It feels strange, that a MouseMove event would change the default cursor shape, since there is Control::get_cursor_shape for such cases, in which a Control-Node displays different cursor shapes.

[akien-mga]

Thanks!