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/Bytecode/Interpreter.cpp

@@ -136,7 +136,7 @@ Interpreter::ValueAndFrame Interpreter::run_and_return_frame(Executable const& e
 
     if constexpr (JS_BYTECODE_DEBUG) {
         for (size_t i = 0; i < registers().size(); ++i) {
-            String value_string;
+            DeprecatedString value_string;
             if (registers()[i].is_empty())
                 value_string = "(empty)";
             else