fix android support

In order to support android, we need to build the [Android Webrtc codebase](https://chromium.googlesource.com/chromium/src/+/master/docs/android_build_instructions.md) with our necessary changes (to facilitate an IL2cpp compatible interface). In order to do this, the differences from the [webrtc-uwp](https://github.com/webrtc-uwp/webrtc-uwp-sdk) and [webrtc](https://webrtc.googlesource.com/src/+/refs/heads/master/) codebases must be reconciled. Since that work will need to be done in the future (when webrtc-uwp and webrtc decide to merge, assuming they do), we've opted to not do that work now.

__TL;DR: Unity Android/IOS support isn't functional at this time, as there isn't an easy way to apply the uwp changesets that modify the plugin api to the android/ios codebase.__

Start with the linked Android WebRTC build instructions and compare the webrtc-uwp and upstream webrtc codebases, focusing on the changes needed for an IL2cpp-compatible plugin interface. Done means Unity Android and iOS support is functional with the required API changes reconciled across the codebases.

Written by the indexing model from the issue text.