Add nullability support for CarrierConfigLoader class

Follow the Android API guideline at
go/android-api-guidelines#nullability to annotate all non-primitive Java
arguments and return types with nullability.

Bug: 185129900
Test: atest CarrierConfigLoaderTest
Merged-In: Ia366727690ae451e4c8936b5907213f651aecd36
Change-Id: Ia366727690ae451e4c8936b5907213f651aecd36
(cherry picked from commit fe0d7c1cb61bdec0f228d0e3f36c8bf7baa3aadb)
1 file changed