Add monospace toggle button to textarea (#24034)

- Add new button to textarea to switch font. State is persisted in
localStorage.
- Change markdown-switch-easymde button from `<span>` to `<button>`
- Slightly increased monospace font globally by 5% as I think it fits
better.

For hover effect on these buttons I'm deferring to
https://github.com/go-gitea/gitea/pull/23896.


![](https://user-images.githubusercontent.com/115237/230948526-ecf8d730-0c69-4a8e-a1a5-1e5e079c754d.gif)

---------

Co-authored-by: delvh <dev.lh@web.de>

templates/shared/combomarkdowneditor.tmpl

@@ -40,12 +40,18 @@ Template Attributes:
 				<md-ref class="markdown-toolbar-button" data-tooltip-content="{{.locale.Tr "editor.buttons.ref.tooltip"}}">{{svg "octicon-cross-reference"}}</md-ref>
 			</div>
 			<div class="markdown-toolbar-group">
+				<button class="markdown-toolbar-button markdown-switch-monospace" role="switch" data-enable-text="{{.locale.Tr "editor.buttons.enable_monospace_font"}}" data-disable-text="{{.locale.Tr "editor.buttons.disable_monospace_font"}}">{{svg "octicon-typography"}}</button>
 				<button class="markdown-toolbar-button markdown-switch-easymde" data-tooltip-content="{{.locale.Tr "editor.buttons.switch_to_legacy.tooltip"}}">{{svg "octicon-arrow-switch"}}</button>
 			</div>
 		</markdown-toolbar>
 		<text-expander keys=": @">
 			<textarea class="markdown-text-editor js-quick-submit"{{if .TextareaName}} name="{{.TextareaName}}"{{end}}{{if .TextareaPlaceholder}} placeholder="{{.TextareaPlaceholder}}"{{end}}{{if .TextareaAriaLabel}} aria-label="{{.TextareaAriaLabel}}"{{end}}>{{.TextareaContent}}</textarea>
 		</text-expander>
+		<script>
+			if (localStorage?.getItem('markdown-editor-monospace') === 'true') {
+				document.querySelector('.markdown-text-editor').classList.add('gt-mono');
+			}
+		</script>
 	</div>
 	<div class="ui tab markup" data-tab-panel="markdown-previewer">
 		{{.locale.Tr "loading"}}