Android: Switch to UniFFI experimental FFI

[bendk]

We've been developing this in to try to reduce the Android crash rate. We're not sure if this will work or not, so the plan is to run an experiment where we switch to a UniFFI branch with the new FFI and monitor the crash rate. The branch is based off of 0.31 and should only affect Kotlin/Android.

https://docs.google.com/document/d/13kEAIcjoHYVH-z4uKFsTsLKaUc1I-PmZ_E-Orn2lgqY/edit?tab=t.0#heading=h.rjnszvtvhr7e mozilla/uniffi-rs#2765

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