Everywhere: Rename {Deprecated => Byte}String

This commit un-deprecates DeprecatedString, and repurposes it as a byte
string.
As the null state has already been removed, there are no other
particularly hairy blockers in repurposing this type as a byte string
(what it _really_ is).

This commit is auto-generated:
  $ xs=$(ack -l \bDeprecatedString\b\|deprecated_string AK Userland \
    Meta Ports Ladybird Tests Kernel)
  $ perl -pie 's/\bDeprecatedString\b/ByteString/g;
    s/deprecated_string/byte_string/g' $xs
  $ clang-format --style=file -i \
    $(git diff --name-only | grep \.cpp\|\.h)
  $ gn format $(git ls-files '*.gn' '*.gni')

Tests/LibCore/TestLibCoreArgsParser.cpp

@@ -115,7 +115,7 @@ TEST_CASE(bool_option)
 TEST_CASE(positional_string_argument)
 {
     // Single required string argument
-    DeprecatedString name = "";
+    ByteString name = "";
     auto parser_result = run_parser({ "app"sv, "buggie"sv }, [&](auto& parser) {
         parser.add_positional_argument(name, "name", "name", Core::ArgsParser::Required::Yes);
     });