Show outdated comments in files changed tab (#24936)

If enabled show a clickable label in the comment. A click on the label
opens the Conversation tab with the comment focussed - there you're able
to view the old diff (or original diff the comment was created on).

**Screenshots**


![image](https://github.com/go-gitea/gitea/assets/1135157/63ab9571-a9ee-4900-9f02-94ab0095f9e7)

![image](https://github.com/go-gitea/gitea/assets/1135157/78f7c225-8d76-46f5-acfd-9b8aab988a6c)



When resolved and outdated:

![image](https://github.com/go-gitea/gitea/assets/1135157/6ece9ebd-c792-4aa5-9c35-628694e9d093)

Option to enable/disable this (stored in user settings - default is
disabled):

![image](https://github.com/go-gitea/gitea/assets/1135157/ed99dfe4-76dc-4c12-bd96-e7e62da50ab5)

![image](https://github.com/go-gitea/gitea/assets/1135157/e837a052-e92e-4a28-906d-9db5bacf93a6)



fixes #24913

---------

Co-authored-by: silverwind <me@silverwind.io>

templates/repo/diff/options_dropdown.tmpl

@@ -14,5 +14,20 @@
 		{{end}}
 		<a id="expand-files-btn" class="item">{{.locale.Tr "repo.pulls.expand_files"}}</a>
 		<a id="collapse-files-btn"class="item">{{.locale.Tr "repo.pulls.collapse_files"}}</a>
+		{{if .Issue.Index}}
+			{{if .ShowOutdatedComments}}
+				<a class="item" href="?style={{if $.IsSplitStyle}}split{{else}}unified{{end}}&whitespace={{$.WhitespaceBehavior}}&show-outdated=false">
+					<label class="gt-pointer-events-none">
+						{{.locale.Tr "repo.issues.review.option.hide_outdated_comments"}}
+					</label>
+				</a>
+			{{else}}
+				<a class="item" href="?style={{if $.IsSplitStyle}}split{{else}}unified{{end}}&whitespace={{$.WhitespaceBehavior}}&show-outdated=true">
+					<label class="gt-pointer-events-none">
+						{{.locale.Tr "repo.issues.review.option.show_outdated_comments"}}
+					</label>
+				</a>
+			{{end}}
+		{{end}}
 	</div>
 </div>