Replace PageLoader.getPage() with PageLoader.loadPage() (#8976)

* Follow page status via StateFlow

Keep getPage subscription since it's needed to load the pages

* Replace PageLoader.getPage with PageLoader.loadPage

(cherry picked from commit 2ef1f07aaea0852c13a4eb4096ac96c8aa507c39)

# Conflicts:
#	app/src/main/java/eu/kanade/tachiyomi/ui/reader/loader/HttpPageLoader.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerPageHolder.kt

source-api/src/main/java/eu/kanade/tachiyomi/source/model/Page.kt

@@ -21,10 +21,14 @@ open class Page(
         get() = index + 1
 
     @Transient
-    @Volatile
-    var status: State = State.QUEUE
+    private val _statusFlow = MutableStateFlow(State.QUEUE)
+
+    @Transient
+    val statusFlow = _statusFlow.asStateFlow()
+    var status: State
+        get() = _statusFlow.value
         set(value) {
-            field = value
+            _statusFlow.value = value
             statusSubject?.onNext(value)
         }