Bug 15597 – error messages in mixins should show context

We need to find a better way of giving errors from mixins. For instance: icomponent.d-mixin-48(55): Error: found '<' when expecting ')' This tells me nothing, and to proceed I need to start adding pragma(msg, ...) in strategic places to try and discover what I'm actually dealing with. Suggest: Errors in mixins print a context to the error output, that is, the line of text the compiler is trying to compile, and perhaps even 1-2 lines before/after the context line if they look interesting.

This predates the fix for https://issues.dlang.org/show_bug.cgi?id=12790 in 2.084.0 does that solve this issue?