Fix reaction color for non-emojis on dark theme

Hardcoding it to black is bad for dark themes. It was probably done
because the default color would make emojis look pale due to
transparency. If we use a primary text color which hopefully does not
feature transparency (it does not for SC themes, at least), everything
looks fine.

Change-Id: I207290a777086db1b27209c4dc34a9810be0a37c

vector/src/main/res/layout/reaction_button.xml

@@ -45,7 +45,7 @@
         android:maxEms="10"
         android:minWidth="20dp"
         android:singleLine="true"
-        android:textColor="@color/emoji_color"
+        android:textColor="?vctr_content_primary"
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintEnd_toStartOf="@id/reactionCount"
         app:layout_constraintHorizontal_chainStyle="packed"