Some dirs and files are not packed by `l3build ctan`

[muzimuzhi]

Brief outline of the bug

In a glance,

• pgf_3.1.9a.tds.zip contains 148 directories, 918 files
  • At that time .tds.zip is generated by lua function generate_CTANzip in build.lua.
• pgf_3.1.10.tds.zip contains only 92 directories, 642 files

Among the differences some are resulted from https://github.com/pgf-tikz/pgf/pull/1095 but apparently some important files are really not packed by l3build ctan. To list some,

• source dir (well, already aware of, see https://tug.org/pipermail/pgf-tikz/2023q1/000083.html)
• doc/generic/pgf/licenses dir (It's a fault to drop them.)
• doc/generic/pgf/plots dir
• files in doc/generic/pgf/images not matched by doc/generic/pgf/images/*.jpg, especially pgfmanual-mindmap-1.pdf and pgfmanual-mindmap-2.pdf

Need to play (or struggle) with l3build variables further more.

Minimal working example (MWE)

not required

[muzimuzhi]

l3build manifest can be helpful.