docs(splitter): Persist pane size in the persisted layout story

[jsakamotoIGJP]

Description

First of all, thank you for working on this feature. I tried the new PersistedLayout story, and the collapse/expand events worked very nicely.

However, I noticed that the story only saves and restores the collapsed state. The pane size is not restored after a reload. Since the story is named "Persisted Layout", I think saving the pane size too would make it a better example of real world usage.

So this PR extends the story to also save and restore startSize by listening for the igcResizeEnd event. The story description in the docs is updated accordingly. There is no change to the component itself, only to the story.

Type of Change

• Documentation update

Related Issues

Related to #2297 and #2299 (this PR targets the rkaraivanov/splitter-collapsed-panes-state branch)

Testing

I ran Storybook locally and checked the PersistedLayout story in Chrome:

1. Drag the splitter bar, then reload the page. The pane size is restored.
2. Collapse a pane, then reload the page. The collapsed state is restored, as before.
3. Clear localStorage and reload. The story starts from the default 50% layout.

Checklist

• My code follows the project's coding standards
• I have tested my changes locally
• I have updated documentation if needed

[Copilot]

Pull request overview

This PR updates the Splitter Storybook documentation story PersistedLayout to persist and restore the pane size in addition to the collapsed state, making the example closer to real-world persisted layout usage.

Changes:

• Update the story docs description to mention persisting startSize and listening for igcResizeEnd.
• Read persisted startSize from localStorage and bind it to .startSize.
• Persist startSize alongside startCollapsed/endCollapsed on resize/expansion events.