Fix 21530 - dtoh: Sanitize identifiers wrt. reserved C++ keywords

[MoonlightSentinel]

Extends the check for C++ keywords to append an underscore instead of
raising an error whenever the actual name doesn't matter for binary
compatibility.

CC @kinke @ibuclaw

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21530	normal	dtoh: Identifiers need to be sanitized wrt. reserved C++ keywords

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#12122"

[ibuclaw]

Could we just not emit parameter names? They are just superfluous information at best.

[kinke]

Sanitizing here as well makes sense IMO, especially as all comments are stripped, so documentation is scarce already.

[RazvanN7]

Hmmm, maybe it would be useful if we could generate the documentation for the C++ headers also? We could simply paste the initial comment

[MoonlightSentinel]

(Rebased to resolve the merge conflicts)