Add reactivity experiment

[tinykite]

What this does

This update adds a global vue store to test out cross-island interactivity between legacy code and new Vue components. Notable updates:

• Added an additional test component, HelloWorldB to make sure that updates to Vue's store are shared across components.
• Added JavaScript to dashboard.js to test out that we can listen to updates to the Vue store outside of Vue — and similarly make calls to update it as well.
• Added a POC for how we might handle multiple types of updates to the Vue store. Right now, we're only handling dispatches to increment the store's count.

Screenshot

This small experiment provides three different buttons to increment the store's count (one Vanilla JS, two rendered by Vue)

Clicking any of the buttons should update all three counts:

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 71.22%. Comparing base (b51bc33) to head (a2fed03). Report is 6 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #3487 +/- ## ======================================== Coverage 71.22% 71.22% ======================================== Files 48 48 Lines 6512 6512 ======================================== Hits 4638 4638 Misses 1874 1874 ```

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