Rich text editor "expanded mode" (#1656)

* Fix composer icon in dark mode

* Add RTE poc

* Amend cornerRadius

* Add snaps

* Fix composer top spacing

* Fix clipping

* Refine UX

* Fix animation

* Add constants + iPad hide bars logics

* Polish clamping

* Fix UT

* Cleanup

* Add grabber color

* Add UI tests

* Rename handle -> grabber

* Fix resize composer when RTE is off

* Fix project file

ElementX/Resources/Assets.xcassets/colors/grabber.colorset/Contents.json

@@ -0,0 +1,38 @@
+{
+  "colors" : [
+    {
+      "color" : {
+        "color-space" : "srgb",
+        "components" : {
+          "alpha" : "1.000",
+          "blue" : "199",
+          "green" : "197",
+          "red" : "197"
+        }
+      },
+      "idiom" : "universal"
+    },
+    {
+      "appearances" : [
+        {
+          "appearance" : "luminosity",
+          "value" : "dark"
+        }
+      ],
+      "color" : {
+        "color-space" : "srgb",
+        "components" : {
+          "alpha" : "1.000",
+          "blue" : "89",
+          "green" : "83",
+          "red" : "81"
+        }
+      },
+      "idiom" : "universal"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}