Fields don't group edits

[NeilFraser]

To Reproduce

Steps to reproduce the behavior:

1. Choose a new angle with the mouse.
2. Undo several times

Actual behavior

The angle steps back in 15 degree increments one by one.

Expected behavior

The angle should return to 0 (or whatever the initial value was) in a single undo step.

[NeilFraser]

Looking at this again, this appears to be a major regression across all fields, not just the angle field.

Text, number and angle fields in old versions of Blockly group edits just fine:
https://2-dot-blockly-games.appspot.com/turtle?lang=en&level=10
But the current version of Blockly has no grouping.