WebAssembly target for EXT_meshopt_compression support

[yzsolt]

The C++ implementation can target WebAssembly with vertex buffer decoding/filtering and index buffer decoding, which are needed for the EXT_meshopt_compression glTF extension, supported by e.g. three.js and Babylon.js.

Given Rust's excellent WASM support it shouldn't be too difficult to do the same with meshopt-rs.

WASM SIMD support is tracked in a separate issue: https://github.com/yzsolt/meshopt-rs/issues/1