Record module type statistics

Creates a build_system_stats.txt build artifact that contains statistics
on how many BUILD_* modules are defined in a build. Also writes out
information about the Soong module types sent from the Soong build.

Merged-In: Iaf0c7062f542dc6942b5349854f3d49267cac4a5
Change-Id: Iaf0c7062f542dc6942b5349854f3d49267cac4a5