fix: delete assets permanently deleted instead of trash in android R

[shenlong-tanwen]

Changes made

The current implementation of trashing the asset instead of deleting it in Android 30 and above feels inconsistent with the rest of the behavior of the API in older versions of Android and iOS where the asset is irrevocably deleted.

It is changed in this PR to have the same behavior of deleting the asset using MediaStore.createDeleteRequest which based on the documentation calls ContentResolver#delete similar to the handling used in older android versions

Possible improvements

A new method named trashAsset can be added as an feature which would trash the asset instead of deleting it in Android 30 and above along with a method to fetch such assets as well

[shenlong-tanwen]

Fixed the Android CI failing due to the lack of namespace in the example app's build.gradle as well

[CaiJingLong]

I need to see the change on the emulator of different version, I will test this modification in the near future.

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A new method named trashAsset can be added as an feature which would trash the asset instead of deleting it in Android 30 and above along with a method to fetch such assets as well

Introducing new dart api is really a good idea.

[CaiJingLong]

This is a behavior change, although it does not involve breaking the API, but I will put it in the 2.8 version.