Always pass 6-digit hex color to monaco (#25780)

Monaco can not deal with color formats other than 6-digit hex, so we
convert the colors for it via new
[`tinycolor2`](https://github.com/bgrins/TinyColor) dependency (5kB
minzipped).

Also, with the addition of the module, we can replace the existing
`hexToRGBColor` usage, I verified it is compatible with the current
tests before removing the function.

Fixes: https://github.com/go-gitea/gitea/issues/25770

web_src/js/components/ContextPopup.vue

@@ -26,7 +26,8 @@
 <script>
 import $ from 'jquery';
 import {SvgIcon} from '../svg.js';
-import {useLightTextOnBackground, hexToRGBColor} from '../utils/color.js';
+import {useLightTextOnBackground} from '../utils/color.js';
+import tinycolor from 'tinycolor2';
 
 const {appSubUrl, i18n} = window.config;
 
@@ -77,7 +78,7 @@ export default {
     labels() {
       return this.issue.labels.map((label) => {
         let textColor;
-        const [r, g, b] = hexToRGBColor(label.color);
+        const {r, g, b} = tinycolor(label.color).toRgb();
         if (useLightTextOnBackground(r, g, b)) {
           textColor = '#eeeeee';
         } else {