Overhaul update-bcd.ts

[queengooborg]

The update-bcd script is in dire need of an overhaul. It has become too complicated and not easy to maintain, so bugs are challenging to squash. The script should be rewritten from the ground up in a multi-stage process.

[foolip]

mdn/browser-compat-data#19971 moved this script into BCD and some enhancements are planned. Would it make sense to remove the script from this repo instead after confirming the changes made are exactly the same?

[Elchi3]

As discussed in the BCD call, the script should remain in the collector and we should port the overhaul from BCD to this repo.

[Elchi3]

#801 rewrote it using generators and also improved the speed drastically. I think we can close this issue?