Test Week - FolderAccessibilityHelperTest

Adding unit tests for FolderAccessibilityHelper. In order to write these tests we have also included a refactor of DragAndDropAccessibilityDelegate to get mDragLayer and the accessibility delegate from ActivityContext instead of Launcher. This allows us to pull that from test context in ActivityContextWrapper during testing.

* Tests 1 class previously untested
* Tests 3 methods
* Includes 1 class refactor

Bug: 353303621
Test: FolderAccessibilityHelperTest
Flag: TEST_ONLY

Change-Id: I8d13113fc09d3ee902faecc426deb80bcbae0b0d