Make @comapeo/core's tests shareable with core-react-native

[gmaclennan]

Context

Milestone-doc nice-to-have. We re-implement a lot of behaviour that core already tests; running (a subset of) core's tests against the RPC-bridged manager would catch divergence between core and the bridge.

Scope (to refine)

• Investigate making core's tests runnable against core-react (and then core-react against core-react-native).
• assert polyfill for the Jasmine-based React Native test runner.
• Decide which core suites are meaningful across the IPC boundary.

Depends on / relates to the backend test infrastructure (#38) and the e2e suite.