Add a Kati-based packaging step

The idea is that we'd move the installation and packaging tasks over to
it, using data from Soong & the Kati reading Android.mk files.

This would allow us to make more fundamental changes about how we
package things without having to adjust makefiles throughout the tree.
Possible use cases:

* Moving some information from Soong's Android.mk output to a file read
  by the packaging step may allow us to read the Android.mk files less
  often, speeding up builds.

* Refactoring our current two-stage ASAN builds to run the Kati build
  step twice, writing into different object directories, then have a
  single packaging step that reads both outputs. Soong already has the
  capability of writing out a single ninja file with all the asan
  combinations.

* Running two build steps, one building the system-related modules
  using a "generic" device configuration, and one building the vendor
  modules using a specific device configuration. This could enforce a
  GSI/mainline system vs vendor split in a single build invocation.

* If all installation is through this tool, it will be much easier to
  track what should no longer be installed on an incremental build,
  reducing the need for installclean.

* Changing PRODUCT_PACKAGES should be a much faster operation, which
  means we could keep track of local additions to the images. Then
  `mma` would be more persistent, instead of installing something once,
  then never updating it again.

Eventually we plan on switching from Kati to something Go-based, but
this is a more incremental approach while we clean up everything else.

Currently, this just moves the dist-for-goal handling over to the
packaging step, so that we don't need to read Android.mk files when
DIST_DIR changes, or we switch between dist vs not.

Bug: 116968624
Bug: 117463001
Test: m nothing
Change-Id: Idec5ac6f7c7475397ba0fb65bd3785128a7517df
diff --git a/ui/build/environment_test.go b/ui/build/environment_test.go
index 0294dac..37f500f 100644
--- a/ui/build/environment_test.go
+++ b/ui/build/environment_test.go
@@ -56,6 +56,15 @@
 	}
 }
 
+func TestEnvAllow(t *testing.T) {
+	initial := &Environment{"TEST=1", "TEST2=0", "TEST3=2"}
+	initial.Allow("TEST3", "TEST")
+	got := initial.Environ()
+	if len(got) != 2 || got[0] != "TEST=1" || got[1] != "TEST3=2" {
+		t.Errorf("Expected [TEST=1 TEST3=2], got: %v", got)
+	}
+}
+
 const testKatiEnvFileContents = `#!/bin/sh
 # Generated by kati unknown