add mesh public doc-strings

[bjlittle]

🚀 Pull Request

Description

This PR adds the doc-strings to the public API methods of the class iris.experimental.ugrid.Mesh et al.

To view the rendered doc-strings for this pull-request, see here.

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Consult Iris pull request check list

[trexfeathers]

Thanks @bjlittle!

These docstrings are clear, informative and appropriately mirror phrasing in the UGRID conventions.

I've picked up on some corrections that are needed.

As mentioned in specific comments on the code, I have trouble with the level of repetition between the filter methods, their singular equivalents and the remove methods. As I read/scroll through the rendered docs this repetition makes it much harder to keep my place. I like the pattern currently used for documenting Cube.coord() as a solution.

[trexfeathers]

Thanks for the latest clarifications @bjlittle. Here are some final requests in light of my improved understanding. Once these are addressed I'll be delighted to merge 😊

[trexfeathers]

Amazing work as usual @bjlittle, LGTM

[bjlittle]

@trexfeathers Hallelujah 💯 🚀 🥳

Thanks for sticking with it 🍻