Support platform_apis property

Add a platform_apis property.  The logic to verify it isn't
hooked up yet, but this will allow translating modules to
Soong without losing the annotation.

Test: m checkbuild
Change-Id: I75ff2d7b94247873f5bb1547a9b347a8e73c3191

java/java.go

@@ -171,6 +171,9 @@ type CompilerDeviceProperties struct {
 	// if not blank, set to the version of the sdk to compile against
 	Sdk_version *string
 
+	// if true, compile against the platform APIs instead of an SDK.
+	Platform_apis *bool
+
 	Aidl struct {
 		// Top level directories to pass to aidl tool
 		Include_dirs []string