Matched text diagnostics should be in a new attribute

Currently when we have `--matched-text-diagnostics` enabled we add this diagnostics directly in the `matched_text` attribute for the match. This is problematic as this `matched_text` is important in many downstream cases like generating attribution, showing diffs etc, and so this should be in a new attribute `matched_text_diagnostics`.
There would be a downside of increased file size for the result file btw.