Pass annotation processors to kotlinc

Enable the kotlin-annotation-processing plugin and pass annotation
processors to it.

Bug: 122251693
Test: m checkbuild
Test: TestKapt in kotlin_test.go
Change-Id: I841df454beaaa7edd263eea714ca0d958a03c9de
diff --git a/android/config.go b/android/config.go
index 393382b..956c4af 100644
--- a/android/config.go
+++ b/android/config.go
@@ -241,6 +241,7 @@
 	}
 
 	config.BuildOsVariant = config.Targets[BuildOs][0].String()
+	config.BuildOsCommonVariant = getCommonTargets(config.Targets[BuildOs])[0].String()
 
 	return testConfig
 }