Use static initializer for CUJ mapping

To make the intention of CUJ_TO_STATSD_INTERACTION_TYPE more clear, and
reduce the risk of incorrect mappings due to CUJs being listed in the
wrong order, replace the static initializer with a static initializer
block in which the key-value pairs are explicitly specified.

Test: FrameTrackerTest
Bug: 162927074
Change-Id: Ieb45b511c89beae020b19482b980f2ad10fb38e9