Bedstead: use proper diff for printing changes in device policies Adding a function to generate a proper diff using longest common subsequence algorithm. Use that function to generate a proper diff for device policy changes. Bug: 348162683 Test: atest NeneTest:com.android.bedstead.nene.utils.StringLinesDiffTest Test: atest HarrierTest Flag: TEST_ONLY Change-Id: Ia58768623f4418d50b7c1da12a3584052247edec