Update lock and group button state when selection changed in CanvasItemEditor

[jsjtxietian]

Fixes #89016

Node3D seems not suffered from this issue.

[KoBeWi]

You could easily supersede the 2D part of #88997 now.

Add a new bool under all_group called has_canvas_item. Set it to true inside if (item) condition and disable buttons based on has_canvas_item (empty selection is handled for free).

[jsjtxietian]

Add a new bool under all_group called has_canvas_item. Set it to true inside if (item) condition and disable buttons based on has_canvas_item (empty selection is handled for free).

Yes, I guess I can wait for this to be merged first and then rebase that pr to keep commits seperate.

[akien-mga]

Thanks!