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')

Userland/Libraries/LibGUI/TextBox.cpp

@@ -68,7 +68,7 @@ void TextBox::add_current_text_to_history()
     m_saved_input = {};
 }
 
-void TextBox::add_input_to_history(DeprecatedString input)
+void TextBox::add_input_to_history(ByteString input)
 {
     m_history.append(move(input));
     m_history_index++;