vue-class-component is likely going to be the biggest pain point to migrating the Tuleap Vue 2 apps to Vue 3.

Even when working in a Vue 2 app there is no need to continue to add components using vue-class-component. The Composition API is (mostly) accessible in Vue 2 and present the same advantages from a typechecking PoV and is easy to migrate to Vue 3 (the Composition API has basically been backported to Vue from Vue 3)

As an example, the Vue 2 app of the testplan plugin is going to be converted. It is a good playground as it covers most of our usages of Vue in Tuleap and it is well tested.

Following steps are expected:

1. Basic setup with the conversion of a component using props
2. Migration of a component using the Vuex state
3. Migrate the remaining components to see if there are other pain points
4. Check if we can use <script setup> without too much trouble
5. Update Tuleap dev docs to stop stop recommending vue-class-component