[clang][DeclPrinter] Fix AST print of curly constructor initializers

DeclPrinter::PrintConstructorInitializers did not consider curly constructor initializers. Any curly constructor initializers (e.g. `A() : Field{}`) was printed with round brackets (e.g. `A() : Field({})`).

https://github.com/llvm/llvm-project/issues/64061

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D156307