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/LibTest/Results.h

@@ -8,7 +8,7 @@
 
 #pragma once
 
-#include <AK/String.h>
+#include <AK/DeprecatedString.h>
 #include <AK/Vector.h>
 
 namespace Test {
@@ -21,15 +21,15 @@ enum class Result {
 };
 
 struct Case {
-    String name;
+    DeprecatedString name;
     Result result;
-    String details;
+    DeprecatedString details;
     u64 duration_us;
 };
 
 struct Suite {
-    String path;
-    String name;
+    DeprecatedString path;
+    DeprecatedString name;
     // A failed test takes precedence over a skipped test, which both have
     // precedence over a passed test
     Result most_severe_test_result { Result::Pass };