* Replace RxJava in extension installer
Replace common downloadsRelay with Map of individual StateFlows
* Drop RxRelay dependency
* Simplify updateAllExtensions
* Simplify addDownloadState/removeDownloadState
Use immutable Map functions instead of converting to MutableMap
(cherry picked from commit 0ac38297f4bdeb83b2d9c8919b89520e9722f35e)
# Conflicts:
# app/src/main/java/eu/kanade/tachiyomi/extension/ExtensionManager.kt