MWLinkNodeInspector: Actually preserve annotations when converting to link annotation

This was implemented, but didn't work because the node was removed
before its annotations were copied.

Also fixed:
* Don't do an unnecessary transaction to change attributes of a node
  we're going to remove anyway.
* Apply the same link href fixups when converting as when not
  (previously, changing the href to 'example.com' and clicking "Add
  label" would break the link in interesting ways).
* Do a single transaction from replacement instead of removal+insertion
  when possible.

Bug: 67377
Change-Id: I0318ae62c799300fb7696506a9736b839e2c8578
Merge "MWLinkNodeInspector: Actually preserve annotations when converting to link annotation"