Add ScrollManager for programmatic control of ScrollViewWithStickyHeader

[gabrielribeiro]

Summary

This PR introduces a ScrollManager class that enables programmatic scrolling within ScrollViewWithStickyHeader. It allows external code (e.g., view models or UI interactions) to scroll to the sticky header or the main content.

Key Changes

• Added ScrollManager with scrollToHeader() and scrollToContent() APIs.
• Updated ScrollViewWithStickyHeader to optionally accept a ScrollManager and register its internal ScrollViewProxy.
• Added .id(...) identifiers to the header and content views for ScrollViewReader compatibility.
• Maintained full backward compatibility — if no ScrollManager is passed, the behavior is unchanged.

Example Usage

private var scrollManager = ScrollManager()

ScrollViewWithStickyHeader(
    scrollManager: scrollManager,
    header: { /* ... */ },
    content: { /* ... */ }
)

Button("Scroll to Header") {
    scrollManager.scrollToHeader()
}

Motivation

I just wanted to programmatically show or hide the header!

Let me know if you'd like any changes, doc, tests... Happy to help!

[danielsaidi]

Wow @gabrielribeiro this looks amazing, thank you! I will merge this into main and release it in a new version tomorrow.

[gabrielribeiro]

Thank you, Daniel! I'm glad that you liked it!!!

[danielsaidi]

Hi @gabrielribeiro

I was going to merge this for the 0.7 release, but see now that my ScrollViewWithStickyHeader changes has caused some merge conflicts. Would you be able to take a look? Sorry for the additional work.

[gabrielribeiro]

Opened a new one due to conflicts: #27