Clarify how to use keyword arguments in FuncAnimation

[oscargus]

PR Summary

Closes #20326

I didn't find a good animation example to modify...

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).

[QuLogic]

Suggested change

	An option to *fargs* is to use `functools.partial`, with the added
	An alternative to *fargs* is to use `functools.partial`, with the added

[story645]

stealing some of the language/constructs from #20358 to make it clearer that partial is an alternative to fargs

[story645]

Suggested change

	arguments can be supplied via the *fargs* parameter. See *fargs* for
	how to use `functools.partial` to supply keyword arguments.
	arguments can be supplied using `functools.partial` or via the *fargs* parameter.

Flipped because I think the functools version is preferred. I think it's gonna be clearer to add the information about partial in this section since it's passed in as the func keyword, Maybe after the required signature, something like:

To pass in a function with positional keywords, set func to the partial function::
      
     func = partial(func, frame, **kwargs)

[story645]

I think if you move the intro of partial up to func, this can be simplified to

Suggested change

	An option to *fargs* is to use `functools.partial`, with the added
	benefit of also supporting keyword arguments. An example is to pass
	something like::
	partial(func, **kwargs)
	as *func*.
	Passing in `functools.partial` as *func* is preferred to passing in *fargs* and supports keyword arguments. See *func* for an example.

[timhoffm]

Wouldn't you normally have the case that you want to set some kwargs explicitly? Then I suggest to make the example more concrete:

Suggested change

	partial(func, **kwargs)
	partial(func, my_kwarg='something')

Maye even show a more complete FuncAnimation call to show this fits in.

[oscargus]

There is also #20358 which solves the same issue. I'll have a look and may go for extending that instead (the importance of linking PRs to issues...).