[Property Editor] JIT survey

[elliette]

We can only use the data provided in the LogStatsFile to trigger a survey: https://github.com/dart-lang/tools/blob/b51f39d01f5a4af33428a0189cd62595c01e23de/pkgs/unified_analytics/lib/src/log_handler.dart#L16

This currently only includes the count of DevTools event. We will need to modify the unified_analytics package to include Property Editor events.

We can then use that as a trigger in the context survey JSON file:

https://github.com/flutter/uxr/blob/6e4b3b5f5ba93036a4e767552bcf817a2bb0319b/surveys/contextual-survey-metadata.json