Generate <intent-filter>s for web app manifest protocol handlers

See https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/URLProtocolHandler/explainer.md for more info.

BTW, currently both good old imperative `registerProtocolHandler()` way and the new declarative `"protocol_handlers"` web app manifest's way are not supported on Android (`chrome://flags/#enable-desktop-pwas-protocol-handling` experimental flag is available only in Chrome on desktop).

So it would be really nice if Bubblewrap parses web app manifest's `"protocol_handlers"` member and generates and adds ``s to Android manifest.