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')

Meta/Lagom/Tools/CodeGenerators/LibWeb/BindingsGenerator/main.cpp

@@ -78,7 +78,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
         builder.append(namespace_);
         builder.append("::"sv);
         builder.append(interface.name);
-        interface.fully_qualified_name = builder.to_deprecated_string();
+        interface.fully_qualified_name = builder.to_byte_string();
     } else {
         interface.fully_qualified_name = interface.name;
     }