Following up from #390, this issue adds the editor-based issue create experience from gh issue create --editor to gh pr create with the acceptance criteria originally covered in #390 (comment):

1. New gh config value that users can enable that would prefer editor experience where applicable
2. New editor experience to gh issue create triggered by new --editor flag or new gh config value
3. New editor experience to gh pr create triggered by new --editor flag or new gh config value
4. Editor experience having some way to capture instruction that can be ignored upon submission
5. Editor experience having some way to cancel creation through empty message
6. Editor experience resulting in a web link to the resulting issue or PR

cc: @notomo @ahmedelgabri