lint: report golangci-lint problems

[bhcleek]

lint: update golangci-lint handling to report compiler problems

lint: add tests for golangci-lint problems

lint: specify which linter's messages are to be filtered

Specify which linter's messages are to be filtered in
s:metalinterautosavecomplete.

Fixes #2700

[orlangure]

As discussed in the linked issue, neither using master nor this code resolves the issue where vim doesn't recognize location of files reported by golangci-lint. Sample output of golangci-lint if executed in command line:

go/src/dir/some_test.go:15:9: mnd: Magic number: 1, in <argument> detected (gomnd)
                g.Add(1)

golangci-lint version

golangci-lint has version v1.23.4-0.20200208200517-6436e9a757ad built from (unknown, mod sum: "h1:ZQIbuRc4WKsTViDsYeCY0eHR9+bgig7JQK8hoaYP9Bw=") on (unknown)

Vim treats the output as regular error messages and appends || on every line.

[bhcleek]

The tests pass on master and the additional test in this PR are also passing (there's several tests to validate golangci-lint's output is handled correctly).

Since what you're seeing is happening on master, can you create a new issue that has clear reproduction steps? I'll need to know your relevant vim-go settings (e.g. g:go_metalinter_enabled) and some code that can be used to duplicate the problem. If the code to duplicate this is already in a publicly available repo, just point me to it.