Shared Libraries - 2023/Q2/O2/KR2 - Plan the Transaction Controller Migration

[xinnanyemm]

Context
The MetaMask extension and mobile applications each maintain separate implementations for most core wallet functionality. These separate implementations are an enormous maintenance burden, and an obstacle to building a more cohesive UX between all clients. By eliminating this duplication we can dramatically decrease the maintenance burden of the client teams and reduce the costs of future integrations.
This effort has been underway for months, and will continue beyond Q1. Progress towards the first milestone (shared controllers) is tracked here. The most substantial tasks in that milestone are the network, transaction, and keyring controller migrations. In the previous two quarters, we completed most of the network controller migration. Last quarter we also worked on the keyring controller migration, completing initial TypeScript migrations and planning tasks.

KR-2: Plan the transaction controller migration

The transaction controller is the last major difference between extension and mobile at the controller level. They differ substantially on their basic features, as well as on performance and network usage. Our goal for this quarter is to audit both transaction controllers and develop a plan for merging them while minimizing disruption to the client teams.

[xinnanyemm]

Merge the transaction controller in this repository with the extension transaction controller.

Details on the exact steps to take will be added later.

This progresses #700