LibWeb: Implement text-transform: math-auto

This is a simple mapping of some code-points to others.

I was going to use a ref test for this, but without knowing that the
font contains the code-points (which SerenitySans does not) we'd be
comparing a series of replacement characters to a series of replacement
characters, which doesn't tell you if they're the right code-points
underneath.

Userland/Libraries/LibWeb/CSS/Enums.json

@@ -384,6 +384,7 @@
     "full-size-kana",
     "full-width",
     "lowercase",
+    "math-auto",
     "none",
     "uppercase"
   ],

Userland/Libraries/LibWeb/CSS/Identifiers.json

@@ -222,6 +222,7 @@
   "mark",
   "marktext",
   "math",
+  "math-auto",
   "max-content",
   "medium",
   "menu",