Fix Issue 21294: Improve unhelpful error message with duplicate named argument in overload set

[shivajigandham]

Fixes #21294

Description

When calling an overload set with a duplicate named argument (e.g., fun(a: 1, a: 2)), the compiler previously reported a generic "none of the overloads are callable" error. This happened because the specific error from resolveNamedArgs was being treated as a supplemental error and then masked by the primary resolution failure.

This PR:

1. Updates checkNamedArgErrorAndReportOverload to check all candidates in an overload set.
2. If all candidates fail with the same named argument error (e.g., "parameter a assigned twice"), it promotes that error to a primary error.
3. Modifies resolveFuncCall to respect these primary errors and avoid printing redundant "none of the overloads are callable" messages.

This results in much clearer diagnostics for duplicate named arguments in overloaded functions.

[dlang-bot]

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Testing this PR locally

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dub run digger -- build "master + dmd#22804"

[rikkimax]

It appears that you may have misunderstood what supplemental messages are.

They are basically additional lines of output.
Formatted slightly differently from non-supplemental messages.