LibWeb: Move ARIA-related code into the Web::ARIA namespace

ARIA has its own spec and is not part of the DOM spec, which is what the
Web::DOM namespace is for (https://www.w3.org/TR/wai-aria-1.2/).

This allows us to stay closer to the spec with function names and don't
have to add the word "ARIA" to identifiers constantly - the namespace
now provides that clarity.

Userland/Libraries/LibWeb/HTML/HTMLSelectElement.h

@@ -60,7 +60,7 @@ public:
 
     DeprecatedString const& type() const;
 
-    virtual Optional<DOM::ARIARoles::Role> default_role() const override;
+    virtual Optional<ARIA::Role> default_role() const override;
 
 private:
     HTMLSelectElement(DOM::Document&, DOM::QualifiedName);