[clang-tools-extra] [clangd] Add designator hints for parenthesis aggregate initialization (PR #170642)

[Yanzuo Liu via cfe-commits]

zwuis wrote:

We can use `CXXParenListInitExpr::getUserSpecifiedInitExprs()` so that we don't need to handle implicit initializations.

https://github.com/llvm/llvm-project/pull/170642