Thread fragment tweaks part 1

mastodon/src/main/res/drawable/divider_inset_16dp.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+	<item android:left="16dp" android:right="16dp">
+		<shape>
+			<solid android:color="?colorM3OutlineVariant"/>
+			<size android:height="0.5dp"/>
+		</shape>
+	</item>
+</layer-list>