Block workspace gestures fail

[ewpatton]

Describe the bug

At the DHA workshops, a few students ran into an issue where the block workspace would stop recognizing mouse up/down gestures. The only way to resume was to reload App Inventor.

Affects

• Designer
• Blocks editor
• Projects Explorer
• Android Companion
• iOS Companion
• Android Compiled APK/AAB
• iOS Compiled IPA
• Buildserver
• Debugging
• Other... (please describe)

Expected behavior

General interactions with the workspace should not cause it to reach a state where the user can no longer do anything.

Steps to reproduce

Unclear. It did not happen to every student, and even for a given student only once during the 90 minute period. My intuition is that it probably has something to do with lexical variable flydowns, where the blocks get destroyed while having an active gesture and then the gesture cannot be cleared because another flydown has opened.

[ewpatton]

@mjgallag This might be something for you to look at in case it also carries over to Blockly v11.

[tanishkadhaybar9]

Can you assign me this. I want to contribute it in

[SusanRatiLane]

Can you assign me this. I want to contribute it in

We prefer new contributors start with our help wanted list: https://github.com/mit-cml/appinventor-sources/issues?q=is%3Aissue%20state%3Aopen%20label%3A%22help%20wanted%22

Also, we prefer to assign only one issue to a contributor until we have a merged PR.