Remove custom scroll behavior, allow scroll physics customization, fix double scroll effects and double scroll bars

[ulusoyca]

Description

Initially, we had a bad practice of hardcoding scroll behaviors and scroll physics in the package. This information has been an internal detail in the main content implementation, and causing confusion to the users.

This PR addresses the following:

• Removes custom DragScrollBehavior from all examples and the main content component in the scroll list.
• Demonstrates how to add a custom scroll behavior to MaterialApp in all of the examples.
• Adds a scrollPhysics field to the ThemeData to enable customizing of the physics in the main content custom scroll view. Adds an example to the ReadMe file for this field.
• Adds DeviceInfo package to the playground example to be able to test different overscroll effects on Android.

Related Issues

• List not scrolling properly #102

Checklist

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This will ensure a smooth and quick review process.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [-] My PR includes tests for all changed/updated/fixed behaviors.
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (melos run analyze) does not report any problems on my PR.
• The package compiles with the minimum Flutter version stated in the pubspec.yaml

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change.
• No, this is not a breaking change.

[TahaTesser]

Overall looks good.

There are a bunch of changes in just one PR including platform related. Preferably splitting these unrelated changes would make easier to test and review

Changes are in place, Taha is on vacation.