Fix to allow comment poster to edit or delete his own comments (#11671)

* bug: fix comment update permision check

No the ui only allow poster to update or delet comment, which
is not reasonable and different with handle logic, this pr
change it to allow poster of comment do it

ref code:
https://github.com/go-gitea/gitea/blob/e8955173a9be1acaa9a3755c37b6059422acda20/routers/repo/issue.go#L1636

https://github.com/go-gitea/gitea/blob/e8955173a9be1acaa9a3755c37b6059422acda20/routers/repo/issue.go#L1681

fix #11663

Signed-off-by: a1012112796 <1012112796@qq.com>

* simplify code

* fix sign in

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lauris BH <lauris@nix.lv>

templates/repo/diff/comments.tmpl

@@ -31,7 +31,7 @@
 				{{end}}
 			{{end}}
 			{{template "repo/issue/view_content/add_reaction" Dict "ctx" $ "ActionURL" (Printf "%s/comments/%d/reactions" $.root.RepoLink .ID) }}
-			{{template "repo/issue/view_content/context_menu" Dict "ctx" $.root "item" . "delete" true "diff" true }}
+			{{template "repo/issue/view_content/context_menu" Dict "ctx" $.root "item" . "delete" true "diff" true "IsCommentPoster" (and $.root.IsSigned (eq $.root.SignedUserID .PosterID))}}
 			</div>
 		</div>
 		<div class="ui attached segment">