Element order changes after exiting VR

[WoodNeck]

If the canvas element is not the only child within its parent / not a last element, the element order can be changed after exiting from the polyfilled XR session.

This can cause an issue where element order is important like some elements should be displayed above other elements.

Of course, this can be bypassed by applying CSS z-index or order to elements, but it would be nice if the polyfill preserve the elements' order.

before

in xr session

after

<canvas> is appended as the last element