testsuite: withShorterPathForNewBuildStore and findDependencyInStore should be more abstract wrt store directory

[mpickering]

withShorterPathForNewBuildStore and findDependencyInStore should live in the TestM monad and the author of the test should be unaware of how the --store-dir argument is passed to cabal.

This would remove the need to explicitly pass the --store-dir option in tests which need withShorterPathForNewBuildStore and also remove the need to explicitly pass the store dir argument to findDependencyInStore. Not passing these arguments is a potential source of bugs.

I have a patch, which I will put up after #9454 is merged.