Enforce hidden apis usage in product(soong)

Only if PRODUCT_ENFORCE_PRODUCT_PARTITION_INTERFACE is set,
every app and java library in product cannot use hidden APIs anymore.

checkSdkVersion() checks if sdk_version of app and library is narrow enough,
checkLinkType() checks every library that app links agianst

Bug: 132780927
Test: m
Test: set PRODUCT_ENFORCE_PRODUCT_PARTITION_INTERFACE, and check whether build
error occurs.
Change-Id: Ic630503b875040f730feda4fef826ed6d71da111
diff --git a/java/aar.go b/java/aar.go
index afe860c..d8db192 100644
--- a/java/aar.go
+++ b/java/aar.go
@@ -520,7 +520,7 @@
 }
 
 func (a *AARImport) sdkVersion() string {
-	return proptools.StringDefault(a.properties.Sdk_version, defaultSdkVersion(a))
+	return String(a.properties.Sdk_version)
 }
 
 func (a *AARImport) systemModules() string {