macOS port using libmpv render API

[Ivshti]

Summary

Inherits from #5 but since we can't use window embedding anymore on macOS we need to re-do it using the render API.

Short to-do list:

• libmpv-rs that supports render API and latest libmpv: https://github.com/ivshti/libmpv-rs
• make sure that building works such that RUSTFLAGS='-L/opt/homebrew/Cellar/mpv/0.39.0/lib/' is not required
• initialize an opengl context using native APIs like https://github.com/mpv-player/mpv-examples/blob/master/libmpv/cocoa-rendergl/cocoa-rendergl.m - we can use Swift/ObjectiveC for this, it would be much easier than Rust - as long as we can combine it easily with rust code in the same repo:
  • some resources, not checked: https://www.reddit.com/r/rust/comments/2nno39/interoperating_between_objectivec_and_rust/ and https://crates.io/crates/swift-rs
  • sdl2 can also be used but the performance hit is big and we better do it native: https://github.com/kohsine/libmpv2-rs/blob/master/examples/opengl.rs
  • event loop is required
• glue together wry on top of an OpenGL context (see https://github.com/Ivshti/wry/blob/dev/examples/transparent.rs)
• make sure resizing works
• implement IPC with wry
• work this together into stremio-shell-ng with working IPC and everything