Enforce newapi check only if min_sdk_version < compile_sdk_version

- NewApi check should be enforced only if min_sdk_version is less than
  the compile_sdk_version (the opposite direction should be a different
  build-time error)
- Change the datatype of *sdkVersion to android.ApiLevel (from string)
  to support version comparisons

Test: go build ./java
Test: no changes in ninja file
Bug: 228956345

Change-Id: Ic408857db7760d912ef4694d2ed72c0b7106eb04