Issue #1668 - Part 1: Implement support for caret-color property.

This CSS property allows input carets (that blinking input cursor you see in text fields), to be given a custom color. This was implemented in Firefox 53, and it was such a minor feature that no one ever missed it, but I don't see any harm in implementing this.

https://bugzilla.mozilla.org/show_bug.cgi?id=1063162

devtools/shared/css/generated/properties-db.js

@@ -2872,6 +2872,7 @@ exports.CSS_PROPERTIES = {
       "box-shadow",
       "box-sizing",
       "caption-side",
+      "caret-color",
       "clear",
       "clip",
       "clip-path",
@@ -5277,6 +5278,28 @@ exports.CSS_PROPERTIES = {
       "unset"
     ]
   },
+  "caret-color": {
+    "isInherited": true,
+    "subproperties": [
+      "caret-color"
+    ],
+    "supports": [
+      2
+    ],
+    "values": [
+      "COLOR",
+      "auto",
+      "currentColor",
+      "hsl",
+      "hsla",
+      "inherit",
+      "initial",
+      "rgb",
+      "rgba",
+      "transparent",
+      "unset"
+    ]
+  },
   "clear": {
     "isInherited": false,
     "subproperties": [