[clang] [clang][ExprConst] Support DesignatedInitUpdateExpr of array type (PR #201000)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic approved this pull request.

I somehow thought this wasn't possible in my testing... I guess I got confused at some point.

LGTM

https://github.com/llvm/llvm-project/pull/201000