Listen for changes in the Contacts database with Kotlin Flow

[vestrel00]

Depending on API design, the core APIs may need to be modified in order to support this.

Think of a way to do this without using Kotlin Flow. In other words, support this functionality in the core module without depending on any frameworks. The Flow extensions should just be that, extensions.

Depending on the amount of work to be done here, it may be best to split this into separate issues once we've determined what to do.