Use gap's --packagedirs instead of symlinking in gaproot

[lgoettgens]

Resolves #1092.

This needs gap-system/gap#5873 to be available in the used GAP. Thus, I only expect the CI with GAP / julia * / GAP master jobs to succeed.

[fingolfin]

This looks good, clean and simple.

But unfortunately it will have to wait some time, until --packagedirs arrives in our GAP... Normally this would have to wait for GAP 4.15, i.e. a couple months... but I guess we could also patch our GAP to already contain this code... But maybe we should first get 0.13.0 released.

[lgoettgens]

Do we want to proceed with this before GAP 4.15 gets released, i.e. with patching gap-system/gap#5873 into GAP_lib_jll? If yes, I can prepare the yggdrasil PR for that.

[fingolfin]

@lgoettgens yes please

I also would like to release GAP 4.14.1 in the next 2-3 weeks (CC @ThomasBreuer) to get some GAP library & package bug fixes (but that's orthogonal)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.50%. Comparing base (fe2abef) to head (c990b2b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1095      +/-   ##
==========================================
- Coverage   74.66%   74.50%   -0.16%     
==========================================
  Files          55       55              
  Lines        4713     4711       -2     
==========================================
- Hits         3519     3510       -9     
- Misses       1194     1201       +7     

Files with missing lines	Coverage Δ
src/GAP.jl	87.09% <100.00%> (+0.31%)	⬆️
src/setup.jl	78.18% <ø> (-7.04%)	⬇️

[lgoettgens]

I had to add a patch containing gap-system/gap#5873 here as well, so we can patch gap stable-4.14 in the CI with GAP CI job.