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/LibJS/Runtime/AsyncGenerator.h

@@ -39,7 +39,7 @@ private:
     Optional<State> m_async_generator_state;               // [[AsyncGeneratorState]]
     ExecutionContextVariant m_async_generator_context;     // [[AsyncGeneratorContext]]
     Vector<AsyncGeneratorRequest> m_async_generator_queue; // [[AsyncGeneratorQueue]]
-    Optional<String> m_generator_brand;                    // [[GeneratorBrand]]
+    Optional<DeprecatedString> m_generator_brand;          // [[GeneratorBrand]]
 };
 
 }