[clang] [CIR][CodeGen] Support DesignatedInitUpdateExpr in constant emission (PR #194238)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I think the array case should be possible to optimize quite a bit by taking advantage of our trailing zeros, but otherwise this seems reasonable.  I didn't spend a lot of time on the tests as Andy seems to have, but I believe this is in the right direction.

https://github.com/llvm/llvm-project/pull/194238