How can I share my bug report with Android devs?
Question 1: How do I get it shared to google drive? I previously
  presumably configured all bug reports to be shared via the Gmail app,
  and I don't see how to override that setting now.


You can download the files which you got in the gmail app and upload them to google drive by selecting those files on your phone. 


  Second, I'm very surprised to see that we're being asked to share a
  Google Drive link publicly to the world. Aren't there
  privacy-sensitive aspects to bug reports?


Bug reports are only there for developers of the app you have a problem with to see the issue/bug you are having. They only disclose what type of phone you have and what problems there are on the bug so they can fix it. 

Secondly, there is no real security risk of sharing a google drive link. It only goes to those you send it to, but granted if you send it to the wrong person, they can be able to see that information. If this happens (reminding again that sharing a bug report is not dangerous and that there is only about a 1% chance of this to happen) then you can delete the link so no further people can access it.