feat: New ui-data-getter and refactor of ui-data's

[GuiLeme]

What does this PR do?

This PR introduces two main changes:

1. Adds a new ui-data-getter
   A utility to fetch UI data on demand — unlike existing reactive hooks, this does not automatically update when data changes. It fetches the current data only when explicitly requested.

2. Refactors existing ui-data logic
   Updates the previous ui-data-hooks structure to integrate seamlessly with the new ui-data-getter. Both now align under a shared goal: providing access to UI-related information, but with different update strategies (on-demand vs. reactive).

Why is this needed?

A key use case is retrieving a snapshot of the current slide with annotations. Doing this reactively (i.e., every time a new annotation is added) would be inefficient — especially in scenarios like a live class with multiple students making changes simultaneously.
This new approach avoids unnecessary computation by allowing a one-time fetch when needed.

Additionally, this design lays the groundwork for flexibility: if reactivity is later desired for specific data (e.g., presentation-whiteboard-current-slide), we can easily expose it as a hook with minimal changes to the core and SDK.

Motivation

As part of the La Suite Numérique docs integration, we need to append a base64-encoded PNG snapshot of the current slide at the end of the document. This feature supports that requirement cleanly and efficiently.

More

Closely related to bigbluebutton/bigbluebutton#23314