Co-Authored-By: ReinUsesLisp <reinuseslisp@airmail.cc>

Co-Authored-By: ReinUsesLisp <reinuseslisp@airmail.cc>

Co-Authored-By: ReinUsesLisp <reinuseslisp@airmail.cc>

i965 (and probably all mesa drivers) require GL_PROGRAM_SEPARABLE when using
glProgramBinary. This is probably required by the standard but it's ignored by
permisive proprietary drivers.

Converts many of the Find* functions to return a std::optional<T> as
opposed to returning the raw return values directly. This allows
removing a few assertions and handles error cases like the service
itself does.

This member function doesn't actually modify instance state, so it can
be marked as a const member function.

This was missed within #2075. Renames the member function to make it
consistent with the rest of the Find* functions.

Co-Authored-By: FernandoS27 <fsahmkow27@gmail.com>