Enable ElmIncompletePatternInspection inspection on the of keyword

[jfmengels]

Very often I (and others) write a case expression like case x of and the plugin is able to infer that there are missing cases and which ones (or that you need a _ branch).

When I finish to write the of keyword, to make use of the inspection and automatic fixes, I have to go back to the case keyword. Instead, I'd like to have fixes from the of keyword where my editor cursor is at that moment. The of keyword is also more accessible by mouse because you can click anywhere on the line after the of keyword, but having to go to case requires more precision.

This PR makes the inspections available on case available also on of.

[pravdomil]

see #757

[cies]

I'll merge this. Nice improvement!

[jfmengels]

One downside of this if I'm not mistaken, is that this duplicates the incomplete pattern error in the errors panel. Another possibility is to put the underline on the entire case ... of section (possibly spanning a lot of code).

If we could find a way to not duplicate the error, that would be nice 🤷‍♂️

[cies]

@jfmengels Could you merge master into that branch? I fixed the CI :)

[cies]

@jfmengels I've tried to merge this in the 5.0.1 branch (which itself is a branch off of master) and there are a bunch of tests that fail because of it, namely:

I have tried to fix them, but it started to take more time than I had available for it... I kind of hope you could take a look at it. :)

Best is to first merge master into this your branch, as most tests on master currently pass (a few I did not manage to fix yet and quite a few are "flaky").