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/LibCrypto/Cipher/Mode/CTR.h

@@ -11,7 +11,7 @@
 #include <LibCrypto/Cipher/Mode/Mode.h>
 
 #ifndef KERNEL
-#    include <AK/String.h>
+#    include <AK/DeprecatedString.h>
 #endif
 
 namespace Crypto {
@@ -105,7 +105,7 @@ public:
     }
 
 #ifndef KERNEL
-    virtual String class_name() const override
+    virtual DeprecatedString class_name() const override
     {
         StringBuilder builder;
         builder.append(this->cipher().class_name());