Fixed#8861
* use ajax on PR review page
* handle review comments
* extract duplicate code
FetchCodeCommentsByLine was initially more or less copied from fetchCodeCommentsByReview. Now they both use a common findCodeComments function instead
* use the Engine that was passed into the method
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>
