Support markdown editor for issue template (#24400)

Fixes #24398

Task:
- [x] Reusing "textarea" like GitHub seems more friendly to users.
- [x] ^V image pasting and file uploading handling.

<details><summary>screenshots</summary>


![image](https://user-images.githubusercontent.com/18380374/235418877-00090552-ebda-411c-8e39-b47246bc8746.png)

![image](https://user-images.githubusercontent.com/18380374/235419073-dc33cad7-7626-4bce-9161-eb205c7384b5.png)
Display only one markdown editor:

![image](https://user-images.githubusercontent.com/18380374/235419098-ee21386d-2b2d-432e-bdb2-18646cc031e7.png)
Support file upload and ^V image pasting

![image](https://user-images.githubusercontent.com/18380374/235419364-7b390fa4-da56-437d-b55e-3847fbc049e7.png)

</details>

---------

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

web_src/js/features/repo-legacy.js

@@ -3,7 +3,7 @@ import {
   initRepoIssueBranchSelect, initRepoIssueCodeCommentCancel, initRepoIssueCommentDelete,
   initRepoIssueComments, initRepoIssueDependencyDelete, initRepoIssueReferenceIssue,
   initRepoIssueTitleEdit, initRepoIssueWipToggle,
-  initRepoPullRequestUpdate, updateIssuesMeta, handleReply
+  initRepoPullRequestUpdate, updateIssuesMeta, handleReply, initIssueTemplateCommentEditors, initSingleCommentEditor,
 } from './repo-issue.js';
 import {initUnicodeEscapeButton} from './repo-unicode-escape.js';
 import {svg} from '../svg.js';
@@ -53,6 +53,13 @@ export function initRepoCommentForm() {
     return;
   }
 
+  if ($commentForm.find('.field.combo-editor-dropzone').length) {
+    // at the moment, if a form has multiple combo-markdown-editors, it must be a issue template form
+    initIssueTemplateCommentEditors($commentForm);
+  } else {
+    initSingleCommentEditor($commentForm);
+  }
+
   function initBranchSelector() {
     const $selectBranch = $('.ui.select-branch');
     const $branchMenu = $selectBranch.find('.reference-list-menu');
@@ -82,19 +89,6 @@ export function initRepoCommentForm() {
     });
   }
 
-  const $statusButton = $('#status-button');
-  $statusButton.on('click', (e) => {
-    e.preventDefault();
-    $('#status').val($statusButton.data('status-val'));
-    $('#comment-form').trigger('submit');
-  });
-
-  const _promise = initComboMarkdownEditor($commentForm.find('.combo-markdown-editor'), {
-    onContentChanged(editor) {
-      $statusButton.text($statusButton.attr(editor.value().trim() ? 'data-status-and-comment' : 'data-status'));
-    },
-  });
-
   initBranchSelector();
 
   // List submits