PR Summary

[ci skip]
[azurepipelines skip]

make fig.canvas.draw() behave similar to fig.draw(fig.canvas.get_renderer()) for non-interactive backends.
attempts to address #16558

I will be making incremental changes (still haven't completely understood the machinery for all the non-interactive backends).

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way