Let notifications use avatar fallback.

Extract code which handles Matrix image to its own api / impl / test modules.

libraries/matrixmedia/test/build.gradle.kts

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2025 Element Creations 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.matrix.ui.media.test"
+}
+
+dependencies {
+    implementation(projects.libraries.matrix.api)
+    implementation(projects.libraries.matrixmedia.api)
+    implementation(projects.libraries.designsystem)
+    implementation(projects.tests.testutils)
+    implementation(libs.coil.compose)
+}