Return ComponentElement from factory methods (#263)

[sundaramramaswamy]

Summary

DataGrid<T>, PropertyGrid, and VirtualList factory methods now return ComponentElement instead of the base Element type.

Why not the typed element (e.g. DataGridElement<T>)?

These factories wrap the typed element record inside a ComponentElement via Component<T,P>(props).WithKey(...). The actual runtime return value has always been ComponentElement — the declared Element return type was just less specific than it could be.

Returning the typed element (DataGridElement<T>) isn't possible without restructuring the Component wrapper pattern. ComponentElement is the most specific accurate type.

Changed files

File	Change
DataGridFactories.cs	Both overloads: Element → ComponentElement
PropertyGridFactories.cs	Element → ComponentElement
VirtualListFactories.cs	Element → ComponentElement
reactor.api.txt (×2)	Return type annotations updated

Fixes #263

[sundaramramaswamy]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved in 7f93653. The conflicts were in both reactor.api.txt files — kept ComponentElement for PropertyGrid (this PR's change) and adopted the updated parameter names (onIsCheckedChanged, onSelectedIndexChanged) that landed on main in the meantime.