Create diff note on specific lines

Background

This is based on @phikai's feedback in #444184 (comment 1846286394):

Could we break up the comments more? For example, the first comment lists A LOT of things, but then is specific about lines... could those just be comments on those lines?

Proposal

Send entire an entire file diff instead of single hunks. Produce line-by-line comments.

See &13008 (comment 1966197290) for a prompt proposal to return line-by-line comments.