Add banner for optional migration to simplified sliding sync (#3429)

* Add banner for optional migration to native sliding sync

- Add `MatrixClient.isNativeSlidingSyncSupported()` and `MatrixClient.isUsingNativeSlidingSync` to check whether the home server supports native sliding sync and we're already using it.
- Add `NativeSlidingSyncMigrationBanner` composable to the `RoomList` screen when the home server supports native sliding sync but the current session is not using it.
- Add an extra logout successful action to the logout flow, create `EnableNativeSlidingSyncUseCase` so it can be used there.

* Update screenshots

* Make sure the sliding sync migration banner has lower priority than the encryption setup ones

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Co-authored-by: ElementBot <benoitm+elementbot@element.io>

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/MatrixClient.kt

@@ -126,4 +126,10 @@ interface MatrixClient : Closeable {
      */
     suspend fun getUrl(url: String): Result<String>
     suspend fun getRoomPreview(roomIdOrAlias: RoomIdOrAlias, serverNames: List<String>): Result<RoomPreview>
+
+    /** Returns `true` if the home server supports native sliding sync. */
+    suspend fun isNativeSlidingSyncSupported(): Boolean
+
+    /** Returns `true` if the current session is using native sliding sync. */
+    fun isUsingNativeSlidingSync(): Boolean
 }