Fix and enhance comment editor monospace toggle (#36181)

Fixes: https://github.com/go-gitea/gitea/issues/36175

1. Correctly apply setting on textareas spawned by comment edit
3. When changing the setting, apply it to all textareas on the current page

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

templates/repo/diff/box.tmpl

@@ -10,7 +10,7 @@
 				</button>
 				<script>
 					// Default to true if unset
-					const diffTreeVisible = localStorage?.getItem('diff_file_tree_visible') !== 'false';
+					const diffTreeVisible = window.localUserSettings.getBoolean('diff_file_tree_visible', true);
 					const diffTreeBtn = document.querySelector('.diff-toggle-file-tree-button');
 					const diffTreeIcon = `.octicon-sidebar-${diffTreeVisible ? 'expand' : 'collapse'}`;
 					diffTreeBtn.querySelector(diffTreeIcon).classList.remove('tw-hidden');