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/LibWeb/XHR/XMLHttpRequest.cpp

@@ -305,7 +305,7 @@ void XMLHttpRequest::set_document_response()
         document = DOM::Document::create(realm());
         if (!charset.has_value())
             if (auto found_charset = HTML::run_prescan_byte_stream_algorithm(*document, m_received_bytes); found_charset.has_value())
-                charset = MUST(String::from_deprecated_string(found_charset.value())).bytes_as_string_view();
+                charset = MUST(String::from_byte_string(found_charset.value())).bytes_as_string_view();
 
         // 5.3. If charset is null, then set charset to UTF-8.
         if (!charset.has_value())