Add support for `v2-install`-ing foreign libraries.

[typedrat]

Closes #6046.

Still needs documentation updates, plus shakedown testing from anyone who isn't me.

With more than two options of "thing that can be installed", existing interface doesn't make sense. Instead of exclusive modes, we now have a flag for each kind of thing that can be installed, allowing the user to select what they want explicitly.

---

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• [x] Patches conform to the coding conventions.
• [x] Any changes that could be relevant to users have been recorded in the changelog.
• [ ] The documentation has been updated, if necessary.
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[typedrat]

I don't understand why there's the test failure... Where is that extra space coming from?

[jneira]

It would be nice if someonr could continue this (it needs a rebase, docs ans tests but is a relative small pr)

[ulysses4ever]

@Mergify rebase

[mergify[bot]]

rebase

❌ Base branch update has failed

Git reported the following error:

Rebasing (1/1)
warning: inexact rename detection was skipped due to too many files.
warning: you may want to set your merge.renamelimit variable to at least 1677 and retry the command.
error: could not apply 542d2f21c... Add support for `v2-install`-ing foreign libraries.
Resolve all conflicts manually, mark them as resolved with
"git add/rm <conflicted_files>", then run "git rebase --continue".
You can instead skip this commit: run "git rebase --skip".
To abort and get back to the state before "git rebase", run "git rebase --abort".
Could not apply 542d2f21c... Add support for `v2-install`-ing foreign libraries.
Auto-merging cabal-install/tests/UnitTests/Distribution/Client/ProjectConfig.hs
Auto-merging cabal-install/changelog
CONFLICT (modify/delete): cabal-install/Distribution/Client/Config.hs deleted in HEAD and modified in 542d2f21c (Add support for `v2-install`-ing foreign libraries.). Version 542d2f21c (Add support for `v2-install`-ing foreign libraries.) of cabal-install/Distribution/Client/Config.hs left in tree.
CONFLICT (modify/delete): cabal-install/Distribution/Client/CmdInstall/ClientInstallFlags.hs deleted in HEAD and modified in 542d2f21c (Add support for `v2-install`-ing foreign libraries.). Version 542d2f21c (Add support for `v2-install`-ing foreign libraries.) of cabal-install/Distribution/Client/CmdInstall/ClientInstallFlags.hs left in tree.
CONFLICT (modify/delete): cabal-install/Distribution/Client/CmdInstall.hs deleted in HEAD and modified in 542d2f21c (Add support for `v2-install`-ing foreign libraries.). Version 542d2f21c (Add support for `v2-install`-ing foreign libraries.) of cabal-install/Distribution/Client/CmdInstall.hs left in tree.

err-code: C1B3F

[Kleidukos]

Marking this PR as draft :slightly_smiling_face: