We chatted about it at the scrum this morning, and came up with two suggested alternatives:

1. (easier, more hacky) Since this is a hack anyway, let's not add anything to core for it; instead, just have the code hints extension stuff a function onto some global (e.g. brackets._jsCodeHints.findDefinition) and have the quick edit extension grab it from there.
2. (more work, less hacky) Just combine JS Quick Edit and JS Code Hints into a single extension (this is what the Typescript extension does). Since there's a strong dependency between them now anyway, there isn't any value in keeping them separate. Probably the easiest way to do this would be to create a single "JavaScriptSupport" extension, put the existing contents of the two extensions into separate folders within that extension, and create a new top-level main.js that loads the two main.js-es from the subfolders. (You'd probably have to do the same thing with unittests.js as well.)

Given that we're near the end of the sprint, (1) is fine for now since it's less work/less risk--we can file a bug to do (2) later on.