[WEB] Need more PageTransitionTheme for web transition

[kwak914]

Use case

Proposal

    pageTransitionsTheme: PageTransitionsTheme(builders: {
      TargetPlatform.iOS: CupertinoPageTransitionsBuilder(),
      TargetPlatform.android: OpenUpwardsPageTransitionsBuilder(),
    }),

Web transition doesn't need those of
-FadeUpwardsPageTransitionsBuilder
-OpenUpwardsPageTransitionsBuilder
-CupertinoPageTransitionsBuilder

I think TranisitionBuilder for web should be supported,

such as NoAnimationTransitionBuilder..

[yjbanov]

This looks like a design language question. It also applies to desktop platforms. I'm removing platform-web tag.

[yjbanov]

/cc @HansMuller

[braj065]

When using Nav 2.0 to achieve a custom transition i am using PageRouteBuilder(transitionBuilder:). But the 'transitionBuilder' isn't accepting 'DualTransitionBuilder' to achieve smoother screen enter/exit animation. So i am adding the custom animation using 'DualTransitionBuilder' in ThemeData 'pageTransitionsTheme'. But there is no TargetPlatform.Web for 'pageTransitionsTheme'. So not able to achieve 'DualTransitionBuilder' in web.