Update ReorderableListView API docs (#69650)

* Update ReorderableListView API docs

* fixed dart fmt

* added dartpad instead of code sample

* fixed parenthesis error

* Update packages/flutter/lib/src/material/reorderable_list.dart

Co-authored-by: Amit Patil <54329870+Amitpatil215@users.noreply.github.com>

* using reference List.generate instead of generate

* request changes are complete

* space eroors are fixed

* Update ReorderableListView API docs

* fixed dart fmt

* added dartpad instead of code sample

* fixed parenthesis error

* using reference List.generate instead of generate

* Update packages/flutter/lib/src/material/reorderable_list.dart

Co-authored-by: Amit Patil <54329870+Amitpatil215@users.noreply.github.com>

* request changes are complete

* space eroors are fixed

* request changes are completes

Co-authored-by: Amit Patil <54329870+Amitpatil215@users.noreply.github.com>
Co-authored-by: John Ryan <ryjohn@google.com>