AK+Everywhere: Rename String to DeprecatedString

We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)

Userland/Libraries/LibWeb/HTML/HTMLSelectElement.h

@@ -56,7 +56,7 @@ public:
     // https://html.spec.whatwg.org/multipage/forms.html#category-label
     virtual bool is_labelable() const override { return true; }
 
-    String const& type() const;
+    DeprecatedString const& type() const;
 
 private:
     HTMLSelectElement(DOM::Document&, DOM::QualifiedName);