Add display item for unknown/file attachments

Co-authored-by: LucasGGamerM <lucassggabriel@gmail.com>

mastodon/src/main/res/drawable/bg_search_button.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<ripple
+	xmlns:android="http://schemas.android.com/apk/res/android"
+	android:color="?android:attr/colorControlHighlight">
+	<item>
+		<shape>
+			<solid android:color="?colorSearchField"/>
+			<corners android:radius="6dp"/>
+		</shape>
+	</item>
+</ripple>