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/LibDNS/Packet.cpp

@@ -141,7 +141,7 @@ Optional<Packet> Packet::from_raw_packet(u8 const* raw_data, size_t raw_size)
 
         auto& record = *(DNSRecordWithoutName const*)(&raw_data[offset]);
 
-        String data;
+        DeprecatedString data;
 
         offset += sizeof(DNSRecordWithoutName);