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/DevTools/HackStudio/FindInFilesWidget.cpp

@@ -17,9 +17,9 @@
 namespace HackStudio {
 
 struct Match {
-    DeprecatedString filename;
+    ByteString filename;
     GUI::TextRange range;
-    DeprecatedString text;
+    ByteString text;
 };
 
 class SearchResultsModel final : public GUI::Model {
@@ -105,7 +105,7 @@ static RefPtr<SearchResultsModel> find_in_files(StringView text)
             builder.append(file.document().text_in_range(range));
             builder.append(0x02);
             builder.append(right_part);
-            matches.append({ file.name(), range, builder.to_deprecated_string() });
+            matches.append({ file.name(), range, builder.to_byte_string() });
         }
     });