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/CMakeLists.txt

@@ -1,6 +1,9 @@
 include(libweb_generators)
 
 set(SOURCES
+    ARIA/ARIAMixin.cpp
+    ARIA/ARIAMixin.idl
+    ARIA/Roles.cpp
     Bindings/AudioConstructor.cpp
     Bindings/CSSNamespace.cpp
     Bindings/FetchMethod.cpp
@@ -75,9 +78,6 @@ set(SOURCES
     DOM/AccessibilityTreeNode.cpp
     DOM/Attr.cpp
     DOM/Attr.idl
-    DOM/ARIAMixin.cpp
-    DOM/ARIAMixin.idl
-    DOM/ARIARoles.cpp
     DOM/CDATASection.cpp
     DOM/CharacterData.cpp
     DOM/CharacterData.idl