Improve modal sheet UX

[fujidaiti]

This PR reworks the core logic of modal sheet and fixes the following long standing issues:

• closes SheetDismissible not working with NavigationSheet #137
• closes Modal sheet is still dismissible by tapping barrier even if the form changes in todo list example app #132
• closes Add a way to handle dismissing modal sheet events in one place #130
• closes SheetDismissible never trigger pull-to-dismiss action if ListView's scroll offset is halfway #84
• closes SheetDismissible not working with infinite looping scroll widget #80
• closes Can't overdrag modal sheet during pull-to-dismiss action #53
• closes Sometimes Pull-to-dismiss action is not triggered on modal sheet #52

Breaking changes

Removed SheetDismissible and added bool swipeDismissible as a replacement for ModalSheetRoute and similar classes like ModalSheetPage and CupertinoModalSheetRoute. See the migration guide for more details.

Internal changes

• Added SheetGestureTamper and TamperSheetGesture.
• Modified ModalSheetRouteMixin to use the TamperSheetGesture widget to handle drag gestures on a modal sheet.

Screenshots

Before:

RocketSim_Recording_iPhone_15_6.1_2024-05-26_16.27.05.mp4

After:

RocketSim_Recording_iPhone_15_6.1_2024-05-26_16.30.59.mp4

[naamapps]

PERFECT!!
Nicely done @fujidaiti 👍