[Doc] Add ACCEPTS for some Axes set methods

[oscargus]

PR summary

If I understand things correctly, this will provide information to the property tables and avoid "unknown".

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines

[timhoffm]

Do you have a link to a property table that is affected?

[oscargus]

New: https://output.circle-artifacts.com/output/job/c73ffe8b-889a-4308-8f90-557401d33a44/artifacts/0/doc/build/html/api/_as_gen/matplotlib.axes.Axes.html#matplotlib.axes.Axes

Old: https://matplotlib.org/stable/api/_as_gen/matplotlib.axes.Axes.html#matplotlib-axes-axes

xbound is one example.

[oscargus]

(I've earlier found these ACCEPTS quite confusing as I didn't understand what they were used for, but then I saw that something happened with xlim and ylim and realized that was exactly what they were doing...)

[timhoffm]

This is good for now.

FYI: The obscure .. ACCEPTS doc comments should be repaced by a decorator in the future, see 2#2699.

[oscargus]

Yes, I agree that they are obscure. But since they solve the problem and there seems to be issues agreeing on the decorator...