Hooks: use the appropriate Cabal unit ID

[sheaf]

This commit updates the logic in Distribution.Client.Dependency.addDefaultSetupDependencies to add an implicit Cabal dependency for the custom setup stanza of packages with build-type: Hooks.

This ensures we always pick a version of Cabal that is compatible with whatever other libraries the custom-setup stanza depends on (such as Cabal-hooks).

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[sheaf]

TODO:

• Add Cabal dependency earlier instead of in SetupWrapper, so that it participates in solving. This handles e.g. the setup stanza only depending on some other package like a Cabal-hooks-API package that re-exports Cabal-hooks
• Testing: use a local noindex repo with two fake Cabal packages, one which is poisoned in some way (e.g. empty) and one which is sufficient to validate we are picking the right Cabal.

[sheaf]

This is now ready for review. The fix is quite simple, but it was quite tricky to write a test case for it! The test works by carefully crafting a package database containing a poisoned version of Cabal that we must not pick. See the T11331 test case.

[geekosaur]

I'm only requesting a comment, so it's otherwise good to go.