Implementing new API : getWindowsOnAllDisplays()

1. Implementing the new API for supporting multi-display.
SparseArray<List<AccessibilityWindowInfo>> getWindowsOnAllDisplays()
2. Modifying the documents of this API and its function is to get the window lists of
default display.
List<AccessibilityWindowInfo> getWindows()

Bug: 133279356
Test: a11y CTS & unit tests
Change-Id: Id4e874f43390bdf4196d106a44bbca18bf9fd1d6