Prototype changes for multitree

This change contains a prototype implementation for multitree.
A new file core/tasks/multitree.mk adds a goal named "update-meta",
which searches for "imported" and "exported" Android.bp modules and
writes a json metadata to track dependencies between components.

Bug: 230448564
Test: m
Change-Id: Ie93e3bf130cacb6b6de41acee3bd302f64f1ab95