[webview_flutter] Add verticalScrollBarEnabled function

[JerryKhw]

This was implemented because a scrollbar disable function was needed.

flutter/flutter#62464

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[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!).

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[cbracken]

Hi @JerryKhw, thanks for your contribution.

Looks like the Dart code fails analysis:

warning - lib/src/webkit_webview_controller.dart:521:16 - The method doesn't override an inherited method. Try updating this class to match the superclass, or removing the override annotation. - override_on_non_overriding_member
   info - lib/src/webkit_webview_controller.dart:521:16 - Missing documentation for a public member. Try adding documentation for the member. - public_member_api_docs

On the iOS side, looks like there are build errors:

Xcode build done.                                           30.4s
Failed to build iOS app
Error (Xcode): ../lib/src/webview_controller.dart:411:21: Error: The method 'verticalScrollBarEnabled' isn't defined for the class 'PlatformWebViewController'.

You'll also need to add tests to ensure that the new behaviour doesn't get regressed by future patches.

I'm going to mark this as a draft PR for now. Once you've resolved these issues and all checkboxes in the above list are ticked, please mark as ready for review and we'll take a look.