dafny: add a timeLimit option and message-parsing

[benknoble]

The option itself was manually tested.

The message-parsing has a new test.

#3390 should probably merge first, which will necessitate some updates to this PR.

[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.

[benknoble]

@w0rp should be passing

[hsanson]

Looks good. Tests in order too and no visible backward compatibility issues.

[benknoble]

@hsanson should we update bufnr to filename now that #3390 is merged, too? I'm actually surprised the tests passed after that

[hsanson]

@benknoble I do not use Dafny but from what I have read it seems using filenames would be useful in this case. It will allow ALE to show errors on files still not open (no buffer) in vim/nvim.