#11531: Autogenerate API rst stub files, add summary table on API page

[yan-zaretskiy]

Ticket

#11531

Problem description

Presently, we have to create an individual .rst file for every op we want to list in the Sphinx documentation. This creates unnecessary friction to adding documentation.

What's changed

• We use Sphinx's autosummary directive to auto-generate rst files for us. This requires us to write an extension that knows how to document FastOperation instances automatically.
• We also remove manual function signatures from all op bindings. This was done so that those signatures get injected into the op documentation. The downside is that we have to make sure that the signature and individual attribute descriptions are in sync (there are currently not), and also it does not play well with the autosummary's generated table on the API page.
• This PR requires that we follow the Google docstring style for documenting ops. It will be merged when all ops have been migrated.

Checklist

• Post commit CI passes