Before, when an OnDiskBitmap was a paletted bitmap type, the palette
was internal to the OnDiskBitmap, and it internally performed the palette
conversion itself. When using with a tilegrid, a ColorConverter() object
always had to be passed.
Now, an OnDiskBitmap has a "pixel_shader" property. If the bitmap is
a paletted bitmap type, it is a (modifiable) Palette object. Otherwise,
it is a ColorConverter() object as before. This allows palette effects
to be applied to paletted OnDiskBitmaps.
Code that used to say:
```python
face = displayio.TileGrid(odb, pixel_shader=displayio.ColorConverter())
```
must be updated to say:
```python
face = displayio.TileGrid(odb, pixel_shader=odb.pixel_shader)
```
Compatible code for 6.x and 7.x can say
```python
face = displayio.TileGrid(odb, pixel_shader=getattr(odb, 'pixel_shader', ColorConverter())
```
We can't handle rgbmatrix's interrupts from here until the display is
reinitialized, so set the display as paused.
With this change, I can survive multiple cycles with wifi+rgbmatrix
on an esp32s2. Before, it usually failed.
This also removes the need to pin share because we don't use the
status LED while user code is running.
The status flashes fallback to the HW_STATUS LED if no RGB LED is
present. Each status has a unique blink pattern as well.
One caveat is the REPL state. In order to not pin share, we set the
RGB color once. PWM and single color will be shutoff immediately but
DotStars and NeoPixels will hold the color until the user overrides
it.
Fixes#4133
Unify USB-related makefile var and C def as CIRCUITPY_USB.
Always define it as 0 or 1, same as all other settings.
USB_AVAILABLE was conditionally defined in supervisor.mk,
but never actually used to #ifdef USB-related code.
Loosely related to #4546
