Improve `outdated` support for nix-local-build

[hvr]

Here's some ideas for how to improve cabal outdated with the nix-local-build UI in mind:

• cabal outdated should support target-selectors like new-build et al:

  cabal outdated all would then iterate over all local packages configured in cabal.project and check all components for over-constricted bounds.

  And it also makes sense to limit outdated to some components, i.e. if only care about a few components (and e.g. not the testsuite): cabal outdated lib:foo exe:doo would only check the two named components in whichever local package they're located.

  Conversely, we have special names to e.g. refer to all testsuites in the target-selector; so you could also say cabal outdated tests to iterate over all test-suite components in your cabal.project.

• cabal outdated already supports cabal.project.freeze; however, it would be convenient to have a variant which consults the last computed install-plan (and possibly compute one if it's needs (re)computation); IOW, a variant that combines cabal new-freeze with cabal outdated --new-freeze-file but without generating/overwriting an existing cabal.project.freeze file.

/cc @phadej @23Skidoo