`Run` related timing-specific rendering bug w/definition drop-down

This one is an edge case. In at least BSL and ISL+, if I have a file with a goodly number of definitions on a single line, then clicking the (define ...) drop-down within an epsilon of hitting the Run button causes the menu to fail to display, and hangs evaluation.

I discovered this when playing around with a students' file with more than one definition on a given line and investigating the consequences of the (clever!) approach to graphically indicating subsequent definitions on one line.

It may not be a consequence of the multiple definitions, but that's the only way I can reliably trigger it. I also don't know that this strictly limited to the teaching languages, but that's the only condition in which I've been able to trigger it.

I attach a screencap, because it's otherwise difficult to explain the process. I use ⌘+R to trigger the run, so I can get my mouse to the drop-down in time.

https://user-images.githubusercontent.com/1329370/197363369-861168af-1679-4c4f-9bfe-abe8b3a545eb.mov

Start by reproducing the timing described in the issue: use BSL or ISL+ with multiple definitions on one line, then trigger Run while opening a definition drop-down. The fix is complete when the menu reliably displays and evaluation does not hang in this scenario; the payload names no files or tests to inspect.