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/LibRegex/RegexParser.cpp

@@ -9,9 +9,9 @@
 #include "RegexDebug.h"
 #include <AK/AnyOf.h>
 #include <AK/CharacterTypes.h>
+#include <AK/DeprecatedString.h>
 #include <AK/GenericLexer.h>
 #include <AK/ScopeGuard.h>
-#include <AK/String.h>
 #include <AK/StringBuilder.h>
 #include <AK/StringUtils.h>
 #include <AK/TemporaryChange.h>
@@ -74,7 +74,7 @@ ALWAYS_INLINE Token Parser::consume(TokenType type, Error error)
     return consume();
 }
 
-ALWAYS_INLINE bool Parser::consume(String const& str)
+ALWAYS_INLINE bool Parser::consume(DeprecatedString const& str)
 {
     size_t potentially_go_back { 1 };
     for (auto ch : str) {