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

package-lock.json

@@ -41,6 +41,7 @@
         "sortablejs": "1.15.0",
         "swagger-ui-dist": "5.1.0",
         "throttle-debounce": "5.0.0",
+        "tinycolor2": "1.6.0",
         "tippy.js": "6.3.7",
         "toastify-js": "1.12.0",
         "tributejs": "5.1.3",
@@ -10265,6 +10266,11 @@
       "integrity": "sha512-kRwSG8Zx4tjF9ZiyH4bhaebu+EDz1BOx9hOigYHlUW4xxI/wKIUQUqo018UlU4ar6ATPBsaMrdbKZ+tmPdohFA==",
       "dev": true
     },
+    "node_modules/tinycolor2": {
+      "version": "1.6.0",
+      "resolved": "https://registry.npmjs.org/tinycolor2/-/tinycolor2-1.6.0.tgz",
+      "integrity": "sha512-XPaBkWQJdsf3pLKJV9p4qN/S+fm2Oj8AIPo1BTUhg5oxkvm9+SVEGFdhyOz7tTdUTfvxMiAs4sp6/eZO2Ew+pw=="
+    },
     "node_modules/tinypool": {
       "version": "0.6.0",
       "resolved": "https://registry.npmjs.org/tinypool/-/tinypool-0.6.0.tgz",