Co-Authored-By: Joannah Nanjekye <joannah.nanjekye@ibm.com>

The documented definition was much broader than the real one:
there are tons of characters with general category "Other",
and we don't (and shouldn't) treat most of them as whitespace.

Rewrite the definition to agree with the comment on
_PyUnicode_IsWhitespace, and with the logic in makeunicodedata.py,
which is what generates that function and so ultimately governs.

Add suitable breadcrumbs so that a reader who wants to pin down
exactly what this definition means (what's a "bidirectional class"
of "B"?) can do so.  The `unicodedata` module documentation is an
appropriate central place for our references to Unicode's own copious
documentation, so point there.

Also add to the isspace() test a thorough check that the
implementation agrees with the intended definition.

Add error number 113 EHOSTUNREACH to get_socket_conn_refused_errs()
of test.support.

This file started life as a script, before conversion to a
`unittest` test file.  Clear out some legacies of that conversion
that are a bit confusing about how it works.

Most notably, it's unlikely there's still a good reason to try
to recover from `unicodedata` failing to import -- as there was
when that logic was first added, when the module was very new.
So take that out entirely.  Keep `self.db` working, though, to
avoid a noisy diff.

- Remove use of replacement text in the script
- Make use of the pyvenv.cfg file for prompt value.
- Add parameters to allow more flexibility
- Make use of the current path, and assumptions about where env puts things, to compensate
- Make the script a bit more 'idiomatic' Powershell
- Add script documentation (Get-Help .\.venv\Scripts\Activate.ps1 shows PS help page now