Introduce the library libclat to implement clat functions for jni.
It is helpful for unit test.
makeChecksumNeutral() and its test are moved from ClatdController
without behavior change.
Bug: 212345928
Test: build and boot
atest libclat_test
Change-Id: I1c0981d98141fc1cc07b2d3a0f3cbddf38683ff3