(there were no uses of port_realloc to fix)

bitmapfilter.morph is taken from openmv's imlib.

It is substantially faster than blur/sharpen implemented in ulab,
by up to 10x. It also avoids making many allocations.

 * weight can be any sequence (& test it)
 * improve error message
 * correct documentation of ``mask`` vs copypaste from openmv

This allows operations between channels in an image. It can be used for
the following use cases:
 * Conversion to B&W or sepia
 * Adding color casts
 * Mixing or swapping arbitrary channels
 * Inverting or scaling arbitrary channels

we want it for memento, and maybe for qualia. we can add it elsewhere
later if we want

These boards all previously had camera disabled too.

morph9 is a form of morph which performs 9 different convolutions,
like a version of mix where each coefficient is a (2n+1)x(2n+1) matrix.

Most use cases are covered by morph-then-mix, but some advanced operations
may be more efficient to implement via morph9.

This reduces the time from about 133ms to about 122ms on my test
image on the memento pycamera

a similar change to morph did not produce a performance improvement,
so I didn't include it.

.. and no specific use case for morph9 is known that can't be done
with mix+morph.

Saves ~1800 bytes on Memento

Co-authored-by: Scott Shawcroft <scott@tannewt.org>

.. and update the test accordingly, fixing a bug discovered in the
process.