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
Also fixes a bug where the pretty printer didn't insert
linebreaks for a forest (it assumed a single tree root).
Also further regularises bool and quote formatting.
