feat(virtual-core) add getVirtualIndexesAPI (#920)

Author: KevinVandy

docs/api/virtualizer.md

@@ -286,6 +286,14 @@ type getVirtualItems = () => VirtualItem[]
 
 Returns the virtual items for the current state of the virtualizer.
 
+### `getVirtualIndexes`
+
+```tsx
+type getVirtualIndexes = () => number[]
+```
+
+Returns the virtual row indexes for the current state of the virtualizer.
+
 ### `scrollToOffset`
 
 ```tsx

packages/virtual-core/src/index.ts

@@ -696,7 +696,7 @@ export class Virtualizer<
     },
   )
 
-  private getIndexes = memo(
+  getVirtualIndexes = memo(
     () => {
       let startIndex: number | null = null
       let endIndex: number | null = null
@@ -724,7 +724,7 @@ export class Virtualizer<
           })
     },
     {
-      key: process.env.NODE_ENV !== 'production' && 'getIndexes',
+      key: process.env.NODE_ENV !== 'production' && 'getVirtualIndexes',
       debug: () => this.options.debug,
     },
   )
@@ -814,7 +814,7 @@ export class Virtualizer<
   }
 
   getVirtualItems = memo(
-    () => [this.getIndexes(), this.getMeasurements()],
+    () => [this.getVirtualIndexes(), this.getMeasurements()],
     (indexes, measurements) => {
       const virtualItems: Array<VirtualItem> = []