Add Ability to Check if Cursor is Blinking

adds a method for returning whether the cursor is blinking based on the
current value of the mCancelled property in the Blink class.  This
method is only inteded to be used for testing purposes.

Bug: 228354442
Test: manual, method is called in CtsWidgetTestCases:EditTextTest#
      testSuspendAndResumeBlinkingCursor,
      testCursorBlinkingOnNewActivity_WithFocus,
      testCursorNotBlinkingOnNewActivity_WithoutFocus
Change-Id: I02849f6e105cbfe7af78dfb34ffbf1ebbb4a82ae