graph drawing tool

bugfix

Scenario: make some edits, select some text, make some more edits. Press ctrl-z.

Before this commit, undo would stop at the point of selection and previous edits would become unreachable.

After this commit, both ctrl-z and ctrl-y seem able to span the point of selection.

Created by  Kartik K. Agaram  on December 25, 2022
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