Fix 21225 - preview=dtorfields inserts unnecessary dtor calls...

[MoonlightSentinel]

... in nothrow ctors

Fixed by not inserting the destructor call if the constructor is
nothrow - which makes the generated catch-block unreachable
(unless the ctor violates it's nothrow guarantee - which is UB).

This also saves time & memory spent on generating unused AST elements.

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Note; This should also reduce the amount of breakage introduced by -preview=dtorfields`

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21225	normal	preview=dtorfields inserts unnecessary dtor call in nothrow ctors

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#11692"

[wilzbach]

Looks reasonable, though I wonder why the author that inserted this comments a few lines below didn't think about this obvious distinction when he clearly considered this case:

This differs from the alternate scope(failure) version in that an Exception
is caught rather than a Throwable. This enables the optimization whereby
the try-catch can be removed if ctor.fbody is nothrow.

[MoonlightSentinel]

Probably because he assumed that the try...catch will be optimized away at a later stage, resulting in the same observable behavior as this shortcut.