Fix flaky AccessibilityMagnificationTest

The failure is due to the screenshot window is still
visible on  the screen and it is a focused window.
It leads to unexpected active window.

To fix it we broadcast close-system_dialog intent to
close the screenshot window.

Bug: 189723605
Test: atest CtsAccessibilityServiceTestCases
Change-Id: Ib80a39b7d88d199744932a5888d26f54802e2800
2 files changed