Improve [send/bring]-to-[front/back] metadata (#1444)

* Refine `send-to-back` icon

* Improve metadata

* Revert "Refine `send-to-back` icon"

This reverts commit 4f59705fd4.

icons/bring-to-front.json

@@ -11,7 +11,9 @@
     "over",
     "forward",
     "front",
-    "layer"
+    "overlap",
+    "layer",
+    "order"
   ],
   "categories": [
     "design",

icons/send-to-back.json

@@ -11,7 +11,9 @@
     "under",
     "back",
     "backwards",
-    "layer"
+    "overlap",
+    "layer",
+    "order"
   ],
   "categories": [
     "design",