Platform mapping-based product config

This allows us to set product variables as build settings instead
of loading them from a target's provider, which further allows us
to read product config variables in transitions.

Bug: 287539062
Bug: 269577299
Test: Presubmits
Change-Id: I8497703f706162572ceb3486240e1eb02a37f5f6

android/configured_jars_test.go

@@ -21,7 +21,7 @@ import (
 func TestOverrideConfiguredJarLocationFor(t *testing.T) {
 	cfg := NullConfig("", "")
 
-	cfg.productVariables = productVariables{
+	cfg.productVariables = ProductVariables{
 		ConfiguredJarLocationOverrides: []string{
 			"platform:libfoo-old:com.android.foo:libfoo-new",
 			"com.android.bar:libbar-old:platform:libbar-new",