Escape no longer reverts field edits

[NeilFraser]

Open this ancient version of Blockly:
https://2-dot-blockly-games.appspot.com/turtle?level=10
Edit a number field, type in a big number, then press escape.
The number reverts to its original value.

Open any modern version of Blockly:
https://blockly.games/turtle?level=10
Edit a number field, type in a big number, then press escape.
The number no longer reverts to its original value.

Same with text inputs.

[moniika]

I think this may have been caused by #4351