Add KDoc to six small library API modules

Cover the remaining interfaces of libraries/troubleshoot, libraries/matrixmedia,
libraries/dateformatter, libraries/featureflag, libraries/workmanager and
libraries/mediaviewer, along with their members and parameters.

Behaviours worth recording: NotificationTroubleshootTest reports its outcome
through its state flow rather than by returning, and its quickFix throws unless
the test offers one; DateFormatter.format turns a null timestamp into an empty
string so callers need no null check; ImageLoaderHolder keeps one loader per
session because decrypting room media needs that session's client.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

libraries/troubleshoot/api/src/main/kotlin/io/element/android/libraries/troubleshoot/api/test/NotificationTroubleshootNavigator.kt

@@ -8,6 +8,10 @@
 
 package io.element.android.libraries.troubleshoot.api.test
 
+/**
+ * Lets a troubleshooting test's quick fix send the user to another screen, without the test itself knowing about navigation.
+ */
 interface NotificationTroubleshootNavigator {
+    /** Opens the blocked users screen, so the user can unblock someone whose messages were being filtered out. */
     fun navigateToBlockedUsers()
 }

libraries/troubleshoot/api/src/main/kotlin/io/element/android/libraries/troubleshoot/api/test/NotificationTroubleshootTest.kt

@@ -20,11 +20,36 @@ import kotlinx.coroutines.flow.StateFlow
  * the component they're injected into is bound to [SessionScope] and so should these (https://github.com/ZacSweers/metro/issues/1932).
  */
 interface NotificationTroubleshootTest {
+    /** Position of this test in the list shown to the user; tests run in ascending order. */
     val order: Int
+
+    /** The current state of this test, which the UI observes to show it as idle, running, successful or failed. */
     val state: StateFlow<NotificationTroubleshootTestState>
+
+    /**
+     * Whether this test applies to the current setup, so that irrelevant tests are hidden rather than shown as failing.
+     *
+     * @param data the current push provider and distributor, used to decide relevance.
+     */
     fun isRelevant(data: TestFilterData): Boolean = true
+
+    /**
+     * Runs the test, reporting its outcome through [state] rather than by returning or throwing.
+     *
+     * @param coroutineScope the scope to launch any work that must outlive the call itself.
+     */
     suspend fun run(coroutineScope: CoroutineScope)
+
+    /** Returns the test to its idle state so it can be run again. */
     suspend fun reset()
+
+    /**
+     * Attempts to fix what this test detected, for the tests that can offer it. Throws by default, so check the state's quick fix
+     * flag before calling.
+     *
+     * @param coroutineScope the scope to launch any work that must outlive the call itself.
+     * @param navigator used by the fixes that have to send the user to another screen.
+     */
     suspend fun quickFix(
         coroutineScope: CoroutineScope,
         navigator: NotificationTroubleshootNavigator,