Use RN's Hermes JS engine for faster and leaner performance on Android

[hypest]

React Native's own JS engine, Hermes, is touting faster performance, smaller app footprint both for the JS bundle and the memory consumption.

It's be good if we switch to it, at least for Android. There are some instruction on how to do it in the docs, and this comment on a related ticket also seems useful with additional instructions.

[hypest]

This has been moved forward by #1704, with the exception that using bytecode directly in WPAndroid is not yet enabled.

[hypest]

Leaving a note, in case the bytecode based solution doesn't come to fruition, another path to follow could be to see if using Turbo Modules could help with startup time. Relevant post here.