The m_imageData buffer in the BITMAP_BASE is an
internal implementation - the public API to persist the
data to a stream appears to be SaveImageData - so use that,
which hides the implementation (and generates the image data
"live" when needed).
Remove the public access to the m_imageData buffer as it isn't
needed for public use, and also is misleading.
Also break out the formatting of the data into KICAD_FORMAT,
as it's currently replicated in eeschema/pcb/pagelayout
formatting code.
Fixes: https://gitlab.com/kicad/code/kicad/-/issues/19772
Recommendation is to avoid using the year nomenclature as this
information is already encoded in the git repo. Avoids needing to
repeatly update.
Also updates AUTHORS.txt from current repo with contributor names
There was a gentle mish-mash of booleans, some with
true being left/right and some up/down, and some functions that
can flip in both axes (which is never actually done, and doesn't
really make geometric sense).
Replace all this with the FLIP_DIRECTION enum class, which makes
the intention completely unambiguous.
This also then allows a small scattering of simplifications,
because everything takes the same type and you don't have to
fiddle booleans to fit.
