LibWeb: Replace ARIA role static FlyStrings with an enum

This replaces the FlyStrings for ARIA roles that were constructed in
a [[gnu::constructor]] with a single enum. I came across this as the
DOM inspector was crashing due to a null FlyString for an ARIA role.

After fixing that, I was confused as to why these roles were not an
enum. Looking at the spec there's a fixed list of roles and switching
from references to static strings to an enum was pretty much an
exercise in find and replace :).

No functional changes (outside of fixing the mentioned crash).

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -77,7 +77,7 @@ set(SOURCES
     DOM/Attr.idl
     DOM/ARIAMixin.cpp
     DOM/ARIAMixin.idl
-    DOM/ARIARoleNames.cpp
+    DOM/ARIARoles.cpp
     DOM/CDATASection.cpp
     DOM/CharacterData.cpp
     DOM/CharacterData.idl