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: If23b671dbc77719fd38a9b7ffee6bcf085d30db1