Restore get_renderer function in deprecated tight_layout

lib/matplotlib/tight_layout.py

@@ -1,3 +1,16 @@
 from matplotlib._tight_layout import *  # noqa: F401, F403
 from matplotlib import _api
 _api.warn_deprecated("3.6", name=__name__, obj_type="module")
+
+
+@_api.deprecated("3.6", alternative="figure.canvas.get_renderer()")
+def get_renderer(fig):
+    if fig._cachedRenderer:
+        return fig._cachedRenderer
+    else:
+        canvas = fig.canvas
+        if canvas and hasattr(canvas, "get_renderer"):
+            return canvas.get_renderer()
+        else:
+            from . import backend_bases
+            return backend_bases._get_renderer(fig)