https://google.github.io/styleguide/cppguide.html#Designated_initializers
recommends using designated initializers as does https://abseil.io/tips/172,
but apparently they are a non-standard extension prior to C++20.
For maximum compatibility, avoid using them here.

Fixes #1413

PiperOrigin-RevId: 516892890
Change-Id: Id7b7857891e39eb52132c3edf70e5bf4973755af