Improve audio focus management (#4707)

* Extract Audio focus management to its own modules.

* Request Audio focus when playing a voice message.

* Add missing dependency.
(and remove a duplicated one)

* Request Audio focus when playing a video/audio in the media viewer.

* Pause audio when audio focus is lost.

* Rename class

* Fix tests

* Fix detekt issue.

* Audio focus: let the system handle automatic ducking when playing media.

* Document and update API

* Remove useless space.

libraries/audio/test/build.gradle.kts

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2025 New Vector Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+plugins {
+    id("io.element.android-library")
+}
+
+android {
+    namespace = "io.element.android.libraries.audio.test"
+}
+
+dependencies {
+    api(projects.libraries.audio.api)
+    implementation(projects.tests.testutils)
+}

libraries/audio/test/src/main/kotlin/io/element/android/libraries/mediaplayer/test/FakeAudioFocus.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2025 New Vector Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.mediaplayer.test
+
+import io.element.android.libraries.audio.api.AudioFocus
+import io.element.android.libraries.audio.api.AudioFocusRequester
+import io.element.android.tests.testutils.lambda.lambdaError
+
+class FakeAudioFocus(
+    private val requestAudioFocusResult: (AudioFocusRequester, () -> Unit) -> Unit = { _, _ -> lambdaError() },
+    private val releaseAudioFocusResult: () -> Unit = { lambdaError() },
+) : AudioFocus {
+    override fun requestAudioFocus(
+        requester: AudioFocusRequester,
+        onFocusLost: () -> Unit,
+    ) {
+        requestAudioFocusResult(requester, onFocusLost)
+    }
+
+    override fun releaseAudioFocus() {
+        releaseAudioFocusResult()
+    }
+}