MTC feed merge: feed-scope service_ids duplicated in both calendar_dates tables

[landonreed]

From MTC:

we would like to update all the calender_dates.txt records and their corresponding records in trips,txt file in the active feed. This helps us to resolve a conflict between service_ids with same name in active and future feeds. Please let us know if you have any questions or concerns regarding this request.

Essentially, what we need to do here is check if any service_id shows up in both calendar_dates.txt files. If it does, we should feed-scope the service_id for one of those feeds. We already do this for duplicate service_ids found between the calendars.txt tables, so any service_id that is in both feeds' calendars and calendar_dates will get feed-scoped. Operationally, we probably just need to handle this within constructMergedTable, keeping a record of all service_ids from calendar_dates and feed-scope any dupes. There might be some tricky edge cases here. For example, let's say service_id ABC exists in feed 1 calendars.txt but not in feed 2 calendars.txt, but it exists in both calendar_dates.txt files. We may need to ensure that when writing out the GTFS that if ABC is feed-scoped in feed 1 (e.g., VTA:ABC) that it gets properly written out/feed scoped in calendars.txt. calendars.txt gets processed before calendar_dates, so that might complicate things a bit.

GTFS Feeds:
VTA-Future-Feed-10-3-2019.zip
VTA-Current-Feed_10-3-2019.zip