Introduce afdo

A new configuration rule for sampling PGO. This differs from the
original pgo.go rule in the following ways:
 * Automatic propagation to static dependencies
 * Simpler configuration (just put `afdo: true` to optimsation targets)

http://go/android-afdo

Test: build
Bug: 79161490
Change-Id: Ie194824cd523bca19e10ced41d2078fc598f13b3
diff --git a/android/variable.go b/android/variable.go
index bc93835..7bccc91 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -327,7 +327,8 @@
 
 	NamespacesToExport []string `json:",omitempty"`
 
-	PgoAdditionalProfileDirs []string `json:",omitempty"`
+	AfdoAdditionalProfileDirs []string `json:",omitempty"`
+	PgoAdditionalProfileDirs  []string `json:",omitempty"`
 
 	VndkUseCoreVariant         *bool `json:",omitempty"`
 	VndkSnapshotBuildArtifacts *bool `json:",omitempty"`