[Experimental] Use NanoSTL to remove C++ STL depeneency

[syoyo]

Experiment using NanoSTL https://github.com/lighttransport/nanostl to make c++ STL dependency free.

Advantage

Diet TinyUSDZ runtime obj size. This is beneficial when using TinyUSDZ on WASM/WASI/Emscripten environment.

Faster compilation.

Also make it possible of fast parsing of USD on GPU.

Disadvantage

Possible floating-point precision difference(e.g, xform computation) compared to using system's libm library.

Need to re-design C++ API