Replace gsl::span with std::span

[j9liu]

This updates cesium-native to the latest main, and removes mentions of gsl now that CesiumGS/cesium-native#977 is merged.

[j9liu]

CI is failing for the arm64 Android build because of this:

D:/.ezvcpkg/2024.11.16/installed/arm64-android-unity/include\absl/time/time.h:1762:37: error: invalid operands to binary expression ('std::strong_ordering' and 'const std::strong_ordering')
  if (auto c = lhs_hi <=> rhs_hi; c != std::strong_ordering::equal) 

Strange 🤔 seems like something with our dependencies?

[kring]

That's a bug in Abseil, triggered by a limitation in the old compiler used on Android. I fixed it in Unreal in CesiumGS/cesium-unreal#1539 by adding an overlay port of Abseil that hacks in a fix for the Abseil bug.

[kring]

This is the Abseil bug:
abseil/abseil-cpp#1728

[j9liu]

Thanks for the help @kring . It looks like CI is happy now! 🥲

[kring]

Thanks @j9liu!