... not in new_figure_manager. Otherwise, unpickling a figure fails
with wx if no figure was created previously:

$ MPLBACKEND=wxagg python -c 'from pylab import *; plot(); import pickle; pickle.dump(plt.gcf(), open("/tmp/pkl", "wb"))'
$ MPLBACKEND=wxagg python -c 'import pickle; pickle.load(open("/tmp/pkl", "rb"))'

fails with "wx._core.PyNoAppError: The wx.App object must be created first!"

Because new_figure_manager calls new_figure_manager_given_figure (see
note in backend_template), it doesn't need to copy the instantiation.

Also note that backend_tk was already doing the init in
new_figure_manager_given_figure.

PR Summary

PR Checklist

Tests and Styling

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• New features are documented, with examples if plot related.
• New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).
• Documentation is sphinx and numpydoc compliant (the docs should build without error).