Issue #1673 - Part 2: Make tab-size animatable and fix typos.

There were a few typos in the previous patch and this patch also makes tab-size animatable which didn't really require much of a change at all.

dom/animation/test/mozilla/file_discrete-animations.html

@@ -75,11 +75,6 @@ const gMozillaSpecificProperties = {
     from: "ignore",
     to: "stretch-to-fit"
   },
-  "-moz-tab-size": {
-    // https://drafts.csswg.org/css-text-3/#propdef-tab-size
-    from: "1",
-    to: "5"
-  },
   "-moz-text-size-adjust": {
     // https://drafts.csswg.org/css-size-adjust/#propdef-text-size-adjust
     from: "none",