fix broken seealso docstring entries

[kandersolar]

• Closes DOC: some API reference pages have broken "see also" links #941
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Just a simple sphinx docs PR.

[wholmgren]

If it works, I prefer bare function names when the function is in the same module, but what do you think?

[kandersolar]

I don't feel strongly one way or the other. It is a little clunky to have a bunch of pvlib.submodule. everywhere, but in some cases it might help with clarity, for instance in https://pvlib-python--946.org.readthedocs.build/en/946/generated/pvlib.iam.physical.html, martin_ruiz(), ashrae(), interp(), sapm() would lose the context that sapm() is the IAM part of the SAPM.

If you prefer bare function names, that's fine and I'll update this PR tonight.

[cwhanse]

sapm() would lose the context that sapm() is the IAM part of the SAPM.

Because of the SAPM group of functions, I'd prefer full paths. It's clunky but explicit.

[wholmgren]

Ok, then I suggest merging as is. We can take up library-wide consistency in another issue.

[CameronTStark]

Thanks @kanderso-nrel!