[Clang] Add detailed notes explaining why `is_constructible` evaluates to false (Revert 16d5db7) (#151935)

Adds explanation why `is_constructible` evaluates to false.

This reapplies as-is e476f968bc8e438a0435d10934f148de570db8eb.
This was reverted in 16d5db71b3c38f21aa17783a8758f947dca5883f because of
a test failure in libc++.

The test failure in libc++ is interesting in that, in the absence of
nested diagnostics a bunch of diagnostics are emitted as error instead
of notes, which we cannot silence with `-verify-ignore-unexpected`.

The fix here is to prevent the diagnostics to be emitted in the first
place.
However this is clearly not ideal and we should make sure to deploy a
better solution in the clang 22 time frame, in the lines of
https://discourse.llvm.org/t/rfc-add-a-new-text-diagnostics-format-that-supports-nested-diagnostics/87641/12

Fixes #150601

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Co-authored-by: Shamshura Egor <164661612+egorshamshura@users.noreply.github.com>

0 files changed, 0 insertions, 0 deletions