scripts: Adopted ctx.py-related changes in other result scripts

- Adopted higher-level collect data structures:

  - high-level DwarfEntry/DwarfInfo class
  - high-level SymInfo class
  - high-level LineInfo class

  Note these had to be moved out of function scope due to pickling
  issues in perf.py/perfbd.py. These were only function-local to
  minimize scope leak so this fortunately was an easy change.

- Adopted better list-default patterns in Result types:

    def __new__(..., children=None):
        return Result(..., children if children is not None else [])

  A classic python footgun.

- Adopted notes rendering, though this is only used by ctx.py at the
  moment.

- Reverted to sorting children entries, for now.

  Unfortunately there's no easy way to sort the result entries in
  perf.py/perfbd.py before folding. Folding is going to make a mess
  of more complicated children anyways, so another solution is
  needed...

And some other shared miscellany.

scripts/cov.py

@@ -578,6 +578,9 @@ def table(Result, results, diff_results=None, *,
                                 types[k].ratio(
                                     getattr(r, k, None),
                                     getattr(diff_r, k, None)))))
+        # append any notes
+        if hasattr(r, 'notes'):
+            entry[-1][1].extend(r.notes)
         return entry
 
     # recursive entry helper, only used by some scripts