fix(#Magnification): check window magnification supported for context before unit tests

In WindowMagnificationControllerTest, when setUp we add checking whether the window mode is supported. If it's not supported, we can just skip the test to prevent the tests from running on not supported devices.

Bug: 279820875
Test: atest WindowMagnificationControllerTest
      abtd on target cf_gwear_x86-userdebug
      presubmit
Change-Id: If76ba72c4353ac8d7f3ba98048075800054d9f75