Detectors inside custom circuit gates don't show clicks or go into export sim data

[Strilanc]

Example:

https://algassert.com/quirk#circuit={"cols":[["~54gr"]],"gates":[{"id":"~54gr","circuit":{"cols":[["ZDetector","XDetector"]]}}]}

[Strilanc]

Deferred from v2.3 because it likely requires re-working how the position of a gate is described.