A lot of work happens on the main thread in AndroidWebAuthnTokenManager because any call to JNI methods, such as jni::ObjectArray::New, asserts. This is probably due to the implicit JNI context being main-thread-only, or something similar.

There are explicit context methods that might let us avoid having to move back to the main thread at all, and simplify the thread wrangling.

Note: For the WebAuthn calls, removing calledFrom = "gecko" from @WrapForJNI should let them be called from any thread.