Add metrics.proto as host library.

Build libdrm_metrics_protos_full_host
host library for the metrics_dump tool
in vendor/widevine/libwvdrmengine/tools.

bug: 161783052
bug: 170607430

Test: build android image
Test: build metrics_dump tool
Test: Play movies and TV, Netflix
Change-Id: Ice214b46eedfcd2ef034a5edfdced4f2789d296a