CIRCUITPY_* switches for JSON, RE, etc. Doc cleanup

[dhalbert]

Fixes #4056
Fixes #1911.

• Add CIRCUITPY_BINASCII, CIRCUITPY_ERRNO, CIRCUITPY_JSON, CIRCUITPY_RE, switches to make these non-shared-binding modules be switchable like other features.
• Bring documentation about json, re, and other forrmer u* MicroPython native modules up to date .
• Make "Support Matrix" heading clearer.

[dhalbert]

Confirmed that raspberrypi and esp32-s2 builds still have json, etc. included.

[tannewt]

What do you think about moving them to shared-bindings properly? That'd mean the docs use stubs and would be in circuitpython-stubs too.

[dhalbert]

What do you think about moving them to shared-bindings properly? That'd mean the docs use stubs and would be in circuitpython-stubs too.

I want to do that in the long run:, #1899, #1900, #1901, and will come back to that. I started to do it a while ago but it turned out to be more than a half-day or one-day project. If I remember right there was considerable refactoring involved to separate out the API from the implementation. I think I have a branch stashed away. This is a good intermediate step and fixes the sad state of the doc.

[jepler]

This does what I thought it would have, plus some things I would have forgotten. I did spot one maybe-error, though. Give it a double check.

[jepler]

Thanks!

[jepler]

@dhalbert unfortunately this is failing a build due to lack of space --

Build simmel for fr took 25.47s and failed
make: Entering directory '/home/runner/work/circuitpython/circuitpython/ports/nrf'
Use make V=1, make V=2 or set BUILD_VERBOSE similarly in your environment to increase build verbosity.

245912 bytes used, -152 bytes free in flash firmware space out of 245760 bytes (240.0kB).
41592 bytes used, 89480 bytes free in ram for stack and heap out of 131072 bytes (128.0kB).

I hadn't seen french be the biggest translation before now. I think there are some modules that can be excluded from simmel to get it to fit again.

[jepler]

If it builds, merge it! That should give plenty of headroom.