Use standard C++11 integer types in gtest-port.h.

Remove testing::internal::{Int,Uint}{32,64} in favor of types
guaranteed to be in <cstdint> since C++11.

Tests for built-in integer type coverage are switched from
{Int,Uint}64 to [unsigned] long long, which is guaranteed by
C++11 to exist and be at least 64-bit wide.

PiperOrigin-RevId: 281565263