Disable Window magnification for magnification API

To avoid window magnification and full-screen magniification are both
visible while developers use full-screen magnification API, we disable
window magnification if non-default MagnificationSpec is requested by
the AccessibilityService.

Test: atest com.android.server.accessibility.magnification
manually Test: enable window magnification and use Voice Access to
enable full-screen magnification.
Bug: 146475460

Change-Id: I76e0191f8296ddf48bbf41b8cf78113ed797226b