go-mod.bbclass and gomod:// do not have all sources codes available after do_unpack

[ChenQi <Qi.Chen@windriver.com>]

Hi All,

When I was checking recent nerdctl issue about rm_work failure, I found 
that our gomod handling has some problem.

In short, source codes are not available after do_unpack. They are only 
put in place during do_compile.

I think that's why go-mod.bbclass has:
"""
addtask do_compile before do_populate_lic
"""

But this is quite a workaround. do_populate_lic is not the only one that 
need to have full source codes.

For example, meta/classes/archiver.bbclass needs sources codes. There 
must be other classes that assume sources are there after do_unpack and 
modified sources are there after do_patch.

Another big problem is patching. When source codes are only there at 
do_compile, this means we cannot patch it. But Yocto should have full 
control of the sources, we need to be able to patch any file we want.

In summary, from what I see, the current gomod mechanism does not meet 
Yocto's requirement of fully controlling the sources.

I'm bringing this problem up to have more discussion.

Regards,
Qi