Show outdated comments in files changed tab (#24936)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When resolved and outdated: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>

web_src/css/repo.css

@@ -1702,6 +1702,10 @@
 .repository .diff-box .resolved-placeholder {
   display: flex;
   align-items: center;
+  font-size: 14px !important;
+  height: 36px;
+  padding-top: 0;
+  padding-bottom: 0;
 }
 
 .repository .diff-box .resolved-placeholder .button {
@@ -1728,10 +1732,6 @@
   text-align: center;
 }
 
-.repository .diff-file-box .code-diff {
-  font-size: 12px;
-}
-
 .repository .diff-file-box .code-diff td {
   padding: 0 0 0 10px !important;
   border-top: 0;
@@ -2495,14 +2495,17 @@
   left: 7px;
 }
 
-.comment-header .actions a {
-  margin-right: 0 !important;
+.comment-header .actions a:not(.label) {
   padding: 0.5rem !important;
 }
 
-.comment-header-left > * + *,
-.comment-header-right > * + * {
-  margin-left: 0.25rem;
+.comment-header .actions .label {
+  margin: 0 !important;
+}
+
+.comment-header-left,
+.comment-header-right {
+  gap: 4px;
 }
 
 .comment-body {