Merge pull request matplotlib#24465 from anntzer/ob

Reparametrize offsetbox calculations in terms of bboxes.

Author: ksunden

doc/api/next_api_changes/deprecations/24465-AL.rst

@@ -0,0 +1,10 @@
+``OffsetBox.get_extent_offsets`` and ``OffsetBox.get_extent``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+... are deprecated; these methods are also deprecated on all subclasses of
+`.OffsetBox`.
+
+To get the offsetbox extents, instead of ``get_extent``, use
+`.OffsetBox.get_bbox`, which directly returns a `.Bbox` instance.
+
+To also get the child offsets, instead of ``get_extent_offsets``, separately
+call `~.OffsetBox.get_offset` on each children after triggering a draw.