fix(repeater-native): resolve workaround complexity with empty state support

[Andries-Smit]

Fix: Add empty state configuration for Repeater widget

Problem

When a Repeater displays no data, there is currently no way to show users a meaningful message or placeholder. This creates a poor UX where empty lists appear broken or unresponsive.

As a workaround, developers must create a surrounding context that:

• Manually counts results in advance
• Conditionally shows/hides UI based on the count
• Refreshes the entire context when data changes to zero

This workaround is error-prone and adds unnecessary model complexity.

Solution

Add an emptyListContent configuration property to Repeater, allowing developers to define custom content shown when the list is empty.

This:

• Eliminates the need for manual count logic
• Simplifies the data model
• Provides a consistent UX pattern (aligns with Gallery widget behavior)
• Reduces maintenance overhead

Context

Other data container widgets (ListView, Repeater in scroll context) cannot be safely nested in ScrollViews due to VirtualizedList conflicts. The Repeater is often the only viable option in these scenarios, making the empty state configuration essential for real-world applications.

Reference

This implementation follows the existing pattern in the Gallery widget: https://github.com/mendix/native-widgets/blob/main/packages/pluggableWidgets/gallery-native/src/Gallery.xml#L59