Fix 20916 - Print trace for deprecations triggered inside templates

[Geod24]

This turned out to be way easier than I expected.
@John-Colvin : Want to give this a shot ?

I also think it segv dtoh (and I have an idea where the bug is), but let's see what the auto-tester says...

[dlang-bot]

Thanks for your pull request, @Geod24!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20916	normal	hard to find where a deprecation comes from

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#11839"

[Geod24]

@ibuclaw @kinke : Do you need to access printInstantiationTrace from C++ ? If not, I'll make it extern(D) and final.
The issue is that Classification uses Color (which is an enum of int). dtoh does not like the way Classification is defined.

[kinke]

I'm almost certain LDC doesn't.

[MoonlightSentinel]

What caused this commit?

[Geod24]

It just seems very wrong to have this set only on the templates we show (which can vary depending on -v).
errors has meaning semantic-wise, and the amount of frames we print should not affect the semantic of the code.
I didn't witness anything wrong that prompted the commit, it's just my observation of what should happen.
Note that I believe the diff on test/fail_compilation/deprecations.d (L9 in the old code) is due to this: We don't show the error message twice anymore.

[Geod24]

This should be good to go (there was a spurious Buildkite failure, re-triggered).

[ibuclaw]

Well this pulls in excessive baggage to the compiler front-end.

dmd/dtemplate.d:5972:26: error: undefined identifier ‘Classification’
 5972 |     extern(D) final void printInstantiationTrace(Classification cl = Classification.error)
      |                          ^

Copying over Classification from dmd ad verbatim, but now there's a missing module.

dmd/errors.d:24:13: error: undefined identifier ‘Color’
   24 |     error = Color.brightRed,          /// for errors

This occurs in a non-shareable module, so not a big deal, but just highlighting that maybe an another enum would be better.