Auto merge of #126623 - oli-obk:do_not_count_errors, r=davidtwco

Replace all `&DiagCtxt` with a `DiagCtxtHandle<'_>` wrapper type

r? `@davidtwco`

This paves the way for tracking more state (e.g. error tainting) in the diagnostic context handle

Basically I will add a field to the `DiagCtxtHandle` that refers back to the `InferCtxt`'s (and others) `Option<ErrorHandled>`, allowing us to immediately taint these contexts when emitting an error and not needing manual tainting anymore (which is easy to forget and we don't do in general anyway)

src/diagnostics.rs

@@ -566,7 +566,7 @@ pub fn report_msg<'tcx>(
  let is_local = machine.is_local(frame_info);
  // No span for non-local frames and the first frame (which is the error site).
  if is_local && idx > 0 {
- err.subdiagnostic(err.dcx, frame_info.as_note(machine.tcx));
+ err.subdiagnostic(frame_info.as_note(machine.tcx));
  } else {
  let sm = sess.source_map();
  let span = sm.span_to_embeddable_string(frame_info.span);