This converts the public `uiLayoutAbsolute ` and `uiLayoutAbsoluteBlock`
functions to an object oriented API (an `uiLayout::absolute` and
`uiLayout::absolute_block` respectively), following recent changes.
`uiLayout::absolute` now returns an uiLayout reference instead of a
pointer. New calls to this method should use references too.
Part of: #117604
Pull Request: https://projects.blender.org/blender/blender/pulls/138546