Enable android_app_import to supply framework-res.

By enabling an android_app_import module to supply the
special framework-res module, it becomes possible to
create a split build that excludes the source of over
10,000 files under frameworks/base/core/res, replacing
this source with a prebuilt. However, since other parts
of a monolithic build use the source of framework-res,
this scheme works only if your split build manifest
excludes modules that depend on framework-res source.

Bug: 176851898
Test: lunch aosp_arm64-userdebug && m nothing
Test: new TestAndroidAppImportExportPackageResources
Test: local build without prebuilt framework-res
Test: local build with prebuilt framework-res
Change-Id: If00d9dbc656c8406c038448d09f93f767c1e06d1

java/androidmk.go

@@ -646,6 +646,9 @@ func (a *AndroidAppImport) AndroidMkEntries() []android.AndroidMkEntries {
 					entries.SetString("LOCAL_SOONG_BUILT_INSTALLED", a.dexpreopter.builtInstalled)
 				}
 				entries.AddStrings("LOCAL_INSTALLED_MODULE_STEM", a.installPath.Rel())
+				if Bool(a.properties.Export_package_resources) {
+					entries.SetPath("LOCAL_SOONG_RESOURCE_EXPORT_PACKAGE", a.outputFile)
+				}
 			},
 		},
 	}}