Switch Android to new viaduct backend (second try)

[bendk]

The first attempt failed due to UniFFI FFI errors. We believe that the experimental FFI we're testing should fix this by avoiding passing structs over the FFI via JNA.

The plan is to merge this and monitor FFI errors, hopefully this time we don't get a blow up like last time.

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[moztcampbell]

Trying this again seems reasonable to me.

[bendk]

Thanks! Mark gave the plan a thumbs up yesterday, so I'm just going to go ahead and merge.