[Issue 23466] -verrors=context should not repeat same context for supplemental messages

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23466

--- Comment #2 from Nick Treleaven <nick at geany.org> ---
> Supplemental messages generally have no need to show the source line context

The ones quoted are not useful. There are some that are arguably useful because
they show return type and template constraint where the candidate message
doesn't:

fail_compilation/constraints_func4.d(91): Error: none of the overloads of
template `imports.constraints.overload` are callable using argument types
`!()(int, string)`
    overload(0, "");
            ^
fail_compilation/imports/constraints.d(39):        Candidates are:
`overload(T)(T v)`
void overload(T)(T v) if (N!T);
     ^

So the pull now only hides context for supplemental messages that have the same
context as the previous message.

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