[3.x] Add debug_canvas_item_get_local_bound() function to VisualServer

[lawnjelly]

Useful for debugging hierarchical culling.

Notes

• Forgot to add this as part of [3.x] Canvas item hierarchical culling #68738
• It is super useful for debugging hierarchical culling bugs as it can be used to show the debug bound of a node and all descendants (used in a similar way to debug_canvas_item_get_rect() in [3.x] Fix Polygon2D skinned bounds (for culling) #75612 )
• This is primarily for use by engine devs to debug the engine, rather than for users.
• Now coming in useful for debugging 2D particle bounds which don't seem correct.

[akien-mga]

Needs rebase.

[lawnjelly]

Rebased. 👍

[akien-mga]

Thanks!