Allow specifying end column and end line for errors

[yyoncho]

• backends like lsp-ui could provide that data.

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After:

[claassistantio]

All committers have signed the CLA.

[cpitclaudel]

Did you see #1400 ?

[yyoncho]

Did you see #1400 ?

Yes - but it is stalled for not being backward compatible(unless I am mistaken) so I went for implementation that does not break existing backends(forgot to mention in the PR that a version with one region property could work too but it will require backends to do the (line, column) -> point conversion which might not be efficient). I don't mind rejecting this PR in favour of #1400 - it will for me too.

[yyoncho]

ping?

[cpitclaudel]

Sorry for the delay (and thanks for the ping). I think this might be the most reasonable approach. We can fix the region performance issue at a later point. Let me just go through #1400 to see what else was relevant in that code.

[cpitclaudel]

Closing in favor of #1676. Thanks for the PR.

I went for implementation that does not break existing backends

Note that as written, this PR isn't in fact backwards compatible, because the call to (flycheck-error-end-column err) will fail if err is created by a package compiled with a previous version of flycheck.