Steps to replicate the issue (include links if applicable):

• Import the pinia ResourceLoader module while in RL debug mode/having Vue development mode set
• Start a vite (or others) dev server, e.g. using vite-plugin-mediawiki-userscript
• Enable HMR (hot module reloading) and trigger a store reload

What happens?:
The pinia HMR acceptor errors:

Uncaught (in promise) TypeError: vueDemi.set is not a function
    createSetupStore load.php:1560
    useStore load.php:1836
    Pinia load.php:1228
    accept hmr.ts:77
    fetchUpdate hmr.ts:312
    queueUpdate hmr.ts:277
    queueUpdate hmr.ts:277
    handleMessage client.ts:205
    handleMessage client.ts:203
    setupWebSocket client.ts:91
    setupWebSocket client.ts:90
    <anonymous> client.ts:67

Line 1560 of resources/lib/pinia/pinia.iife.js:

vueDemi.set(hotState.value, key, vueDemi.toRef(setupStore, key));

The pinia attempts to call vueDemi.set, which does not exist because it is usually polyfilled by vue-demi. However, vue-demi is not actually loaded anywhere, and is just replaced with a require( 'vue' ) call by ResourceLoader (see resources/Resources.php in dc17d0e1e42827903b92032dafb8e2ff0800583a). This decision was made in T326174#8533382:

Thankfully, the iife build inlines @vue/devtools-api, and we can provide Vue 3 itself in vue-demi's place.

However, this neglects the usage of vue-demi specific functions set and del, which are used 4 and 3 times respectively in HMR functions (blocked by a DEV guard, and compiled out in .prod.js). There are also 5 usages of set in other parts of the code, but are all safely behind vueDemi.isVue2 (which actually doesn't exist, since it is usually set to false by vue-demi, but evaluates to falsy) checks. This means that no production code is affected by this.

What should have happened instead?:
ResourceLoader inlines/adds the vue-demi module (only 559 bytes unminified, vueuse/vue-demi/lib/v3/index.cjs) to pinia's RL module. This only needs to happen when the dev version of pinia is loaded (i.e., $config->get( MainConfigNames::VueDevelopmentMode ) || $context->getDebug()).

Fixing this would really help the developer experience of using the Vue stack for writing a MW userscript/gadget.

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):
enwiki
Other information (browser name/version, screenshots, etc.):
N/A