change lib-target in haskell-cabal-enum-targets to support multiple library components.

[noinia]

Fixes #1796.

[purcell]

Tests now fail with what looks like a legitimate mismatch — worth taking a look and/or adding new tests to reflect the correct behaviour.

[purcell]

Closing and re-opening to re-trigger CI and get a fresh picture of how this looks.

[purcell]

Test haskell-cabal-enum-targets-1 condition:
    (ert-test-failed
     ((should
       (equal
	'("lib:Test" "test:test-1" "bench:bench-1" "exe:bin-1")
	(haskell-cabal-enum-targets)))
      :form
      (equal
       ("lib:Test" "test:test-1" "bench:bench-1" "exe:bin-1")
       ("Test:Test" "test:test-1" "bench:bench-1" "exe:bin-1"))
      :value nil :explanation
      (list-elt 0
		(arrays-of-different-length 8 9 "lib:Test" "Test:Test" first-mismatch-at 0))))
   FAILED   62/540  haskell-cabal-enum-targets-1 (0.000657 sec) at tests/haskell-cabal-tests.el:16

Is this correct? Should the expected list of targets now be changed?