Generate help file during build rather than as a separate CI step

[Avasam]

This generates and includes the help file in the setuptools build, rather than it being a separate CI-only step as before.

This has the advantage that pip installing from source should now always include the help file.

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Since helpfiles have been restores, that also means that we should theorically be able to update the online doc from GitHub artifacts instead of downloading/installing from PyPI. (I think that'll require merging the workflow files though).

[Avasam]

"but it worked on my machine!"... (and I tried to make sure to test from clean installs !)
I think it has something to do with the import pywin32_bootstrap hack. At least the basic idea of pointing a path file to the build folder works, as its not failing on importing isapi

It's also annoyingly basically the same error as in #2392

[Avasam]

Hang on, help files are back in non-arm64 wheels since Python 309...
I'm betting it's due to a combination of:

• Stop calling setup.py, use a build frontend #2396
• and Fix publishing documentation #2384
• (Maybe but likely not Add test for postinstall #2392)

I'll update the scope of this PR and probably do a separate PR for the now-outdated doc.