finish cl_abap_zip implementation

[larshp]

start added in #359

somewhat possible, needed for both abapGit and abap2xslsx unit testing

[marcellourbani]

Wouldn't it make more sense to implement this in js? I assume it's possible, not really sure.
I'm sure you can implement deflate and ZIP headers in ABAP, but sounds like a lot of work, and pretty dumb (meaning I can think of 12 languages I'd rather use for this use case)

[larshp]

zip can call https://github.com/open-abap/open-abap/blob/main/src/cl_abap_gzip.clas.abap#L31

so its "just" sorting out all the header stuff

open-abap is meant for ABAP developers, so as much of it possible should be ABAP, as such

plus I'd like to avoid adding js dependencies from npm

[larshp]

not needed in this case, but I implemented deflate in all ABAP some years ago = https://github.com/larshp/zazlib