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
3 files changed