Fix quote minimization to deal with edits more comprehensively

* Merge adjacent quote nodes in all cases, not just if they are new.

* There was a FIXME that anticipated this but for some reason, we never
  addressed this. This patch addresses that and also applies the
  transformation even when there is no DOM diff information for reasons
  that have been documented in the algorithm.

* This improves selser serialization in a number of edit scenarios.

* New parser tests with edit changes capture the expectations
  represented in this patch.

  TODO: We still need tests that verify that the merging happens even
  when the DOM has DOM-diff information. To be done in a later patch
  by upgrading the parser tests framework. This is tracked in T72722.

Change-Id: Id85af3c67ea6c77e5e98c0bdbdcd18d9d483acb7