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/LibEDID/DMT.h

@@ -54,7 +54,7 @@ public:
         FixedPoint<16, u32> vertical_frequency_hz() const;
         u32 refresh_rate_hz() const;
 #ifndef KERNEL
-        String name() const;
+        DeprecatedString name() const;
 #endif
     };