Cabal autogen-modules and autogen-includes completion

[rm41339]

Added support for the autogen-modules: field in .cabal file completions inside library, executable, test-suite, and benchmark stanzas and autogen-includes in all relevant stanza types via libExecTestBenchCommons.

Behavior was tested manually in a cabal file.

Closes #4526

[VeryMilkyJoe]

Thank you for the PR!
You will need to rebase your changes on top of the current master branch.
If you have trouble with the rebasing, it might be easier to reset to current master and then cherry pick your commit afterwards.
You will also need to add some tests before we can merge this, you can take some inspiration from #4535 if you want, but please do not copy paste.

[rm41339]

Hi, I updated the changes to reflect on top of the current master branch and added tests as well. Please let me know if there's anything else you'd like me to change!

the tests can be run with: cabal test hls-cabal-plugin-tests --test-options="--pattern autogen"

[rm41339]

Hello, I've made the requested changes.

I apologize for some of the unnecessary edits, I think when I was updating to the latest version some changes got lost. I have reverted them back.

Please let me know if there is an issue with anything else, and thank you for your patience.

[rm41339]

I have caught an error in my commit. My apologies, am fixing it right now. I'm still not quite sure by what you meant about adding autogen-modules to libExecTestBenchCommons?

[VeryMilkyJoe]

Looks good to me now, if the CI is green I think we can merge :)
Just one last nitpick, I think we should rename the testdata/autogen-completion directory to testdata/completion so we can add more testdata for completions there in the future.
You already made the change, adding them both to libExecTestBenchCommons, so no worries, I'm happy now!

[rm41339]

Sounds great, thank you for checking! I've renamed the directory :)

[fendor]

Changes look good to me!