Treat enum_literal completion as error completion when switching on error

[psznm]

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In #2619 completions for errors in switch have been added when error_access is detected.

Proposal is that the example below, when enum_literal is detected, should also suggest the error values.

        const err: error{E1, E2} = undefined;
        switch(err) {
            .<cursor>
        }

Not having to write out the error. and needing only . is extremely pleasant feature.