Switch from ArrayBuffer to ByteArray

[jhugman]

According to The Big O of Code Reviews, this is a O(n) change.

ubrn lowers most types to an ArrayBuffer and then maps it to a jsi::ArrayBuffer, and then on to RustBuffer.
wasm-bindgen maps a Uint8Array on to a Vec<u8>.

In order to lower types to a Uint8Array for WASM and ArrayBuffer for JSI, some amount of bundler violence was needed. Given we're using multiple bundlers to package up the frontend Typescript, and we're not really in control of what bundler the developer uses, this doesn't seem like a viable approach.

Instead, this PR changes ubrn to lower types down to a Uint8Array, so that both WASM and React Native use the same underlying representation of byte arrays.

Unfortunately, jsi doesn't expose API for typed arrays (it may in the future), so we look up the buffer property to get an underlying ArrayBuffer.

On the way back, an object of type { buffer: ArrayBuffer; } is returned, which is enough to make the uniffi work and the typescript compiler think it that a typed array has come back from Rust/C++.

Most of this PR was mechanical refactoring (e.g. ArrayBuffer renamed to UniffiByteArray) but there are enough manual changes which merit it being O(n).

[zzorba]

LGTM

This is probably something we should document in the changelog on the next release, given there's a type change? Should we make a spot to accumulate those?