DOC: add api change

Author: jklymak

doc/api/next_api_changes/deprecations/22345-JK.rst

@@ -0,0 +1,14 @@
+Pending deprecation of layout methods
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The methods `~Figure.set_tight_layout`, `~Figure.set_constrained_layout`,
+are discouraged, and now emit a ``PendingDeprecationWarning`` in favor of
+explicitly referencing the layout engine via
+`figure.set_layout_engine('tight')` and
+`figure.set_layout_engine('constrained')`.  End users should not see the
+warning, but library authors should adjust.
+
+The methods `~Figure.set_constrained_layout_pads` and
+`~Figure.get_constrained_layout_pads` are will be deprecated in favor of
+``figure.get_layout_engine().set()`` and
+``figure.get_layout_engine().get()``, and currently emit a
+``PendingDeprecationWarning``.