Text edits should not dismiss approved reviews

[bluekeyes]

Users often leave "approved" GitHub reviews with comments in the review body. Edits to these comments mark the review as edited, which dismisses it when ignore_edited_comments is set in the policy or in the server.

Editing approved reviews should generally be safe, since they cannot change the overall state of the review. If safe, it would be nice to avoid dismissing reviews in this case. I think the safety criteria are:

1. All rules in the policy enable GitHub reviews
2. No rules in the policy use the github_review_comment_patterns feature
3. The edited review has the "approved" state

(1) and (2) are important because otherwise the text of the review comment could be relevant for approval. There are likely still some reviews that would be safe to keep that would be discarded by this criteria, but this should solve the problem for the most common cases with our internal policies.

I'm not sure how hard it will be to actually implement these checks given the current structure.