Add Support for Combine Publishers

[lightandshadow68]

In v3.0, Couchbase Lite Android has recently added Kotlin Flow support for Document changes, replication changes, query changes. Etc.

Combine extensions support for iOS / macOS would be equally useful, especially when used with SwiftUI development and other combine pipelines.

For example, one use case is to leverage CombineLatest to wait until multiple Combine pipelines have completed before presenting an application's main user interface. This could include simultaneously waiting for the current Replication publisher to emit a status with an activity of idle. A Replication pipeline can also be monitored for authentication errors, Queries can publish a stream of result changes, etc.

[pasin]

Thanks for suggestion. We will need to look into this as one of the candidate for an enhancement feature. Any suggestion about what the functionalities and what API may look like are very welcome.