feat(slice scrollbar): Integrate ViewportSliceProgressScrollbar with customizations and docs (#5960)

Co-authored-by: Dan Rukas <dan.rukas@gmail.com>

extensions/cornerstone/src/customizations/viewportScrollbarCustomization.tsx

@@ -0,0 +1,27 @@
+/**
+ * Default customization values for viewport scrollbar behavior.
+ * The `progress` scrollbar variant is in full mode for stack viewports and
+ * acquisition-plane orthographic viewports.
+ * Otherwise, viewports using the `progress` scrollbar show only the indicator.
+ *
+ * - `viewportScrollbar.variant`: `'progress' | 'legacy'` (default: `'progress'`)
+ * - `viewportScrollbar.showLoadedEndpoints`: show loaded-range endpoint caps in full mode
+ * - `viewportScrollbar.showLoadedFill`: show loaded/cached fill in full mode
+ * - `viewportScrollbar.showViewedFill`: show viewed fill in full mode
+ * - `viewportScrollbar.showLoadingPattern`: show loading pattern in full mode while not fully loaded
+ * - `viewportScrollbar.viewedDwellMs`: delay before marking current image viewed in full mode (ms)
+ * - `viewportScrollbar.loadedBatchIntervalMs`: loaded-state version batch interval in full mode (ms)
+ * - `viewportScrollbar.indicator`: optional custom indicator config
+ */
+export default function getViewportScrollbarCustomization() {
+  return {
+    'viewportScrollbar.variant': 'progress',
+    'viewportScrollbar.showLoadedEndpoints': true,
+    'viewportScrollbar.showLoadedFill': true,
+    'viewportScrollbar.showViewedFill': true,
+    'viewportScrollbar.showLoadingPattern': true,
+    'viewportScrollbar.viewedDwellMs': 0,
+    'viewportScrollbar.loadedBatchIntervalMs': 200,
+    'viewportScrollbar.indicator': {},
+  };
+}