Update Switch.d.ts (facebook#38636)

Summary:
updated type for activeThumbColor prop for Switch component

To help community users with all possible properties

## Changelog:

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--> GENERAL CHANGED - added new prop in type of switch component

Pull Request resolved: facebook#38636

Reviewed By: cortinico

Differential Revision: D47800523

Pulled By: lunaleaps

fbshipit-source-id: 25b22a97a3c02ad01c8100fdd1f3e808f296c14c

packages/react-native/Libraries/Components/Switch/Switch.d.ts

@@ -51,6 +51,11 @@ export interface SwitchProps extends SwitchPropsIOS {
    */
   thumbColor?: ColorValue | undefined;
 
+  /**
+   * Color of the active foreground switch grip.
+   */
+  activeThumbColor?: ColorValue | undefined;
+
   /**
    * Custom colors for the switch track
    *