Support generating install rules in Soong

Support moving some install rules into Soong by allowing Soong to
provide a Makefile containing install rules, and by skipping parts
of base_rules.mk when Soong already created an install rule.

The install rules are exported as a Makefile instead of directly
in Soong's build.ninja file so that base_rules.mk can add dependencies
from the `required` property that are hard to resolve in Soong.

Bug: 204136549
Test: m checkbuild
Change-Id: Ife2964d76469b385e90c0c5f6adf21bd2b5e8bf6