Report and publish code coverage, share integration test lib
Code coverage
This is analogous to wrapland!89 (merged). See there for motivation, details on the solution and possible future advancements.
Shared integration test lib
Here we additionally had to reduce the build size, since GitLab.com has a hard limit of 1G and with recent changes to the way internal plugins are compiled, see for example bc3761fd, the overall size was over that limit what lead us to provided to the autotest job with 1f13551c. But with coverage we need the whole build dir.
Our solution for that is, instead of statically compiling the integration test framework into every test, create it as a shared library. The library won't be installed but can be linked against by our tests in the build directory.
By using a shared library the overall size of the build is reduced by about 50% to 1.3G and the (compressed) artifacts size is only around 300M.