Add chevrons-down-up icons (#344)

* Add alias `unfold` for icon `chevrons-up-down`

* Add icon `chevrons-down-up` and its alias

Alias: `fold`

Related issue: #343

icons/chevrons-down-up.svg

@@ -0,0 +1,13 @@
+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <path d="M7 20l5-5 5 5" />
+  <path d="M7 4l5 5 5-5" />
+</svg>

tags.json

@@ -341,6 +341,10 @@
   "chevrons-down": [
     "arrow"
   ],
+  "chevrons-down-up": [
+    "arrow",
+    "fold"
+  ],
   "chevrons-left": [
     "arrow"
   ],
@@ -351,7 +355,8 @@
     "arrow"
   ],
   "chevrons-up-down": [
-    "arrow"
+    "arrow",
+    "unfold"
   ],
   "chrome": [
     "browser"