Add documentation references to BottomSheetThemeData (#107149)

Co-authored-by: Bruno Leroux <bruno.leroux@gmail.com>

packages/flutter/lib/src/material/bottom_sheet.dart

@@ -61,6 +61,8 @@ typedef BottomSheetDragEndHandler = void Function(
 ///    non-modal "persistent" bottom sheets.
 ///  * [showModalBottomSheet], which can be used to display a modal bottom
 ///    sheet.
+///  * [BottomSheetThemeData], which can be used to customize the default
+///    bottom sheet property values.
 ///  * <https://material.io/design/components/sheets-bottom.html>
 class BottomSheet extends StatefulWidget {
   /// Creates a bottom sheet.

packages/flutter/lib/src/material/scaffold.dart

@@ -1736,6 +1736,8 @@ class Scaffold extends StatefulWidget {
   ///  * [showBottomSheet], which displays a bottom sheet as a route that can
   ///    be dismissed with the scaffold's back button.
   ///  * [showModalBottomSheet], which displays a modal bottom sheet.
+  ///  * [BottomSheetThemeData], which can be used to customize the default
+  ///    bottom sheet property values when using a [BottomSheet].
   final Widget? bottomSheet;
 
   /// If true the [body] and the scaffold's floating widgets should size