FIX: bury import of matplotlib.font_manager

We need to ensure that the sub-module matplotlib.font_manager is imported when
it is used in SclarFormater, however if we import it at the top level we will
get circular imports.

closes matplotlib#22305

Author: tacaswell

lib/matplotlib/ticker.py

@@ -441,8 +441,9 @@ def __init__(self, useOffset=None, useMathText=None, useLocale=None):
             useMathText = mpl.rcParams['axes.formatter.use_mathtext']
             if useMathText is False:
                 try:
-                    ufont = mpl.font_manager.findfont(
-                        mpl.font_manager.FontProperties(
+                    from matplotlib import font_manager
+                    ufont = font_manager.findfont(
+                        font_manager.FontProperties(
                             mpl.rcParams["font.family"]
                         ),
                         fallback_to_default=False,