gen-bounds for more than library stanzas

[puffnfresh]

Running cabal gen-bounds will give bounds for the library in my .cabal file. I would also like to see additional bounds for the executables, test-suites and benchmarks.

[phadej]

It would be also cool if redundant bounds aren't added

i.e. (note no bound on base in tests, because tests depends on the library example)

name example

library
  build-depends:  base ^>=4.12.0.0

test-suite tests
  build-depends: base, example, tasty ^>=1.2.1

[ozkutuk]

With the way cabal check currently works, this results in an awkward situation:

$ cabal check
Warning: These warnings may cause trouble when distributing the package:
Warning: These packages miss upper bounds:
- tasty
- tasty-golden
Please add them, using `cabal gen-bounds` for suggestions. For more
information see: https://pvp.haskell.org/

$ cabal gen-bounds
Resolving dependencies...
Congratulations, all your dependencies have upper bounds!

[ozkutuk]

I realized cabal check no longer generates above warnings for tests (and benchmarks) on master, since #8361 got merged. I still think it may be beneficial for cabal gen-bounds to generate the bounds for these internal targets nonetheless. Would it be counterintuitive for gen-bounds to generate bounds when check doesn't complain about the lack of them? If not, I can try my hand at implementing this.