refactor(atomic): replace @stencil/store with in-house implementation

[alexprudhomme]

https://coveord.atlassian.net/browse/KIT-3815

Why replace this dependency ?

We are replacing stencil with lit and @stencil/store has some functionalities depending on stencil internal functions. It won't work once we begin switching.

The implementation is here #4814 (comment)

Why all the changes for isAppLoaded ?

@stencil/store has a hidden functionality we were unknowingly depending on. There is an stencil subscription that causes automatic rerenders. The subscription listens to every component 'getting' a certain part of the state. It registers those components and whenever that same part of the state is 'set', it triggers a new render of those components. We were depending on it for the loadingFlags part of the state.

In this PR I added createAppLoadedListener which takes in a callback and calls it whenever loadingFlags are empty. In every component that needs to listen to the loading flags, we add a @State isAppLoaded and create the listener to that internal state. Whenever that internal state is re triggered, it rerenders the component.

Alternatives to createAppLoadedListener

1. We could create a decorator. That would mean implement the decorator in both Stencil & Lit. We can always revisit this whenever we implement Lit and figure out something better.
2. We could use Lit signals for this. It is exactly the signal use case.

[github-actions]

Pull Request Report

PR Title

✅ Title follows the conventional commit spec.

Live demo links

• Storybook

• Playwright report

Bundle Size

File	Old (kb)	New (kb)	Change (%)
case-assist	243.8	243.8	0
commerce	355	355	0
search	414.9	414.9	0
insight	406.2	406.2	0
recommendation	256.1	256.1	0
ssr	408.8	408.8	0
ssr-commerce	372.7	372.7	0

SSR Progress

Use case	SSR (#)	CSR (#)	Progress (%)
search	39	44	89
recommendation	0	4	0
case-assist	0	6	0
insight	0	27	0
commerce	0	15	0

Detailed logs

search : buildInteractiveResult
search : buildInteractiveInstantResult
search : buildInteractiveRecentResult
search : buildInteractiveCitation
search : buildGeneratedAnswer
recommendation : missing SSR support
case-assist : missing SSR support
insight : missing SSR support
commerce : missing SSR support