Stop cursor from blinking when not visible

Cursor continues to blink in a text field even when the text field is
not currently visible. This change checks the visibility of the window
that houses the text field in addition to checking if the view is in
focus.

Bug: 228354442

Test: Added logging to the shouldBlink() method ran following steps:
     1: open contacts app
     2: tap add new contact, tap in an edit field
     3: move back to home screen
     4: lock screen, then unlock screen
     5: observed logs written out to logcat console when app not
        visible.
     after change logs no longer printed to console, cursor still blinks
     correctly after app is re-opened or when new field becomes in
     focus.
Test: CtsWidgetTestCases:EditTextTest#
        testCursorNotBlinkingOnNewActivity_WithoutFocus()
	testCursorBlinkingOnNewActivity_WithFocus()
	testSuspendAndResumeBlinkingCursor()
Change-Id: Iad4396e5f7fd810344c711320d65c57ea25eda70