Update the pixel_shader usage of OnDiskBitmap

[lesamouraipourpre]

OnDiskBitmap has had incompatible changes in 7.0.0-alpha.3 - Ref: adafruit/circuitpython#4823
This PR is part of a group of updates for this change - adafruit/circuitpython#4982

This PR updates the library to the combined usage for CP6 & CP7.

Also:
Refactor code referencing CircuitPython 4 & 5
Filled out requirements.txt
Include most of the packages in api.rst.
I can't get docs to build for cpb_gizmo so have left it out of the docs for now.

It has not been tested as I do not have the hardware. I tried testing with the PyPortal example but I am getting this bug (even before changes): adafruit/circuitpython#4985

[jepler]

This seems fine, but I don't know why CI/actions has been having trouble with it. No testing performed.

[lesamouraipourpre]

I've tried pulling this PR into a clean directory and pip install -r requirements.txt is behaving like there is a clashing dependency graph. When it finishes locally, I'll try to figure out what the trigger dependency is.

[lesamouraipourpre]

The problem is adafruit-circuitpython-gizmo. There are requirements changes in it that have been merged but not released - adafruit/Adafruit_CircuitPython_Gizmo@1.3.2...HEAD
I had the HEAD installed with pip install -e . instead of the PyPi version.

[FoamyGuy]

I think the necessary changes in the Gizmo library have been released by now. I re-ran the actions and it is now passing.

These changes look good to me. I tested the simpletest script successfully on a PyGamer with 7.0.0-alpha.4

Thanks for these updates @lesamouraipourpre and for taking care of the old v4 / 5 fallback displayio code.