Add ALEPopulateQuickfix and ALEPopulateLocList

[idbrii]

Resolve #1810.

Add ALEPopulateQuickfix and ALEPopulateLocList. They're not very useful
with ale's default autopopulate behaviour, so their useful configuration
is described in help.

Also fixed an unrelated typo.

Open to changing the command names. I'd suggested ALEShowErrors, but since there's two lists I went with populate. Not sure if it should optionally obey g:ale_open_list. That setting seems mostly for "don't make windows popup automatically", so I don't have a bang variant.

I didn't implement the fancy list target preservation described on the issue. Doing that would improve this feature to keep the list updated while it's displayed, but it seems much more complicated.

[idbrii]

CI failed with:

Ran 5 tests in 0.001s

OK

Something went wrong!
Error: Process completed with exit code 1.

I don't understand how to resolve that or find more info. Maybe it's flakey?

I didn't see the "Custom warnings/errors follow". Fixed.

[idbrii]

Fixed trailing whitespace and made test more comprehensive.

[stale]

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests.
If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.

[idbrii]

@w0rp: I've been using this feature since I implemented it and enjoying it. I have tests and it's working well. Could I get a review? Do you want me to rebase on master first?

[idbrii]

Got another user (on #2866) to confirm this PR works for them too.

[stale]

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests.
If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.

[idbrii]

I'm using this regularly.

I don't love how ALEPopulateQuickfix populates for all open files, but ALEPopulateLocList is very useful.

[stale]

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests.
If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.

[idbrii]

@w0rp Still love to get this reviewed and merged. It has tests and documentation.

[stale]

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests.
If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.

[idbrii]

Bump to unstale.

[w0rp]

This looks like pretty much what I described years ago. I'll merge this.

[w0rp]

Cheers! 🍻

Sorry for not being very active these days. I check random things now and then and I don't have much to add to ALE myself for the moment as it does everything I want it to do for now.