v0.0.0-5924-gb118c15f3

SimulationTarget: don't allocate global std::string objects.

... they have a non-trivial constructor. Use std::string_view
instead as they are wrapping constant strings from the .rodata
segment anyway. That also allows to make them constexpr.

Also use designated initializers for readability.

PiperOrigin-RevId: 676651162