histedit: convert message action into a class This converts the message action into a histeditclass instance, as part of an ongoing effort to refactor histedit for maintainability and robustness.

histedit: convert drop action into a class This converts the drop action into a histeditclass instance, as part of an ongoing effort to refactor histedit for maintainability and robustness.

histedit: convert pick action into a class This converts the pick action into a histeditclass instance, as part of an ongoing effort to refactor histedit for maintainability and robustness. The test output changed because previously pick would only report the commit disappearing if there were no merge conflicts. Now that we've unified the normal and the --continue flows, they act the same and we get the warning even after --continue.

histedit: integrate action class into flow This takes the newly added histeditaction class and integrates it into the histedit run and bootstrapcontinue logic. No actions implement the class yet, but they will be add in upcoming patches.