Deprecate hatch patterns with invalid values

[QuLogic]

PR Summary

I noticed while going over the hatch doc PRs that we don't really validate this. This magically works because we just check for the count of the various hatch characters. Since it used to 'work', this adds a deprecation period over which people can fix their calls.

Also, use the new hatch style reference in the Collection docstring since that's more in line with what the docstring is asking for.

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
• [N/A] Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/next_api_changes/* if API changed in a backward-incompatible way

[dstansby]

Looks 👍 overall. backend_bases.GraphicsContextBase also has a set_hatch, does the same validation need applying there?

[QuLogic]

I didn't expect a user to be calling backend_bases.GraphicsContextBase.set_hatch directly, so that's why I didn't add anything to it.