Add "Cancel" and "Are you sure?" to Password Generation experience

[johnjamesjacoby]

Breaking apart from #WP32589, there are two related enhancements to the password generator that I think improve user experience:

• A "Cancel" button to allow users to undo the generated password
• An "Are you sure?" alert if the user attempts to leave the page after generating a password, but without submitting the form

Patch imminent.

[markjaquith]

In 33364:

Introduce a Cancel button and onUnload warning for password changes.

fixes #33079
props johnjamesjacoby

[johnjamesjacoby]

Alright! Thanks, Mark. Sorry for not including screenshots here. Hopefully the ones on #WP32589 were sufficient.