Add Array.append simplifications

[jfmengels]

Adds Array.append simplifications #174

• [x] Array.append Array.empty array -> array
• [x] Array.append array Array.empty -> array
• [x] Array.append (Array.fromList [ a, b, c ]) (Array.fromList [ d, e, f ]) -> Array.fromList [ a, b, c, d, e, f ]

I extracted listAppendChecks into a generic collectionAppendChecks. I noticed it got very close to collectionUnionChecks and changed the error messages to match collectionUnionChecks because they were nicer.

Now collectionAppendChecks and collectionUnionChecks are pretty much the same check, except that the former tries to combine append [ a ] [ b ] into [ a, b ].

I think we can make that work for dict/set as well in a next step, completely fusing the 2 collection checks. The only difference is that sets and dict need to have the elements added to the end rather than at the beginning, so union (fromList [ a ]) (fromList [ b ]) into fromList [ b, a ]. I'll do that in a follow-up PR.

Can be reviewed commit by commit.

[github-actions[bot]]

The branch can be tried out by running:

elm-review --template jfmengels/elm-review-simplify/preview

[lue-bird]

This has been on my wishlist for some time. Very cool! I love the FromListProperties.

[lue-bird]

I suspect there could be issues with cases like

Array.append ([ 1 ] |> Array.fromList) (Array.fromList [ 2 ])

Would be cool to add tests for these cases

[jfmengels]

I added more tests, it looks like things are working as expected :+1: