Fix UI accessibility transforms and update ordering

[ickshonpe]

Objective

• Bevy UI's accessibility module doesn't set the transform on accessiblity nodes, ignoring scaling and rotation.
• UI accessibility nodes should be updated before bevy_winit updates the accesskit adaptors, otherwise there will be a frames delay.

Solution

Replaced the calc_bounds systems with a new system sync_bounds_and_transforms.

Each accesskit Node corresponding to an AccessibleNode UI entity is now given object-centered coordinates for its bounding rect (instead of window coordinates) and a transform.

Accesskit uses local transforms so if an accessible node also has an accessible parent, its transform has to be recomputed relative to its parent.

Testing

I modified the button example so that accesskit integration is enabled by default and the button is drawn at a 45 degrees angle.

cargo run --example button

Screen readers should only react when the pointer is directly over the rotated button if the changes are working.

The example changes should be reverted before merging.

[andriyDev]

Could you try locally adding #23846 and see if this creates any new ambiguities (any involving this new system)?

[andriyDev]

Actually I ended up doing this myself, and yeah looks like this does indeed resolve the ambiguities!

[mockersf]

The example changes should be reverted before merging.

This was not done