Check system certificate violation for product apks

Only if enforcement option is enable, it makes build error when there is apk located at system partition but signed with system certificate.

Bug: 74699609

Test: m -j

Change-Id: I23c41f2665dd97abac3e77d1c82d81ff91b894eb

android/config.go

@@ -950,6 +950,14 @@ func (c *config) FlattenApex() bool {
 	return Bool(c.productVariables.FlattenApex)
 }
 
+func (c *config) EnforceSystemCertificate() bool {
+	return Bool(c.productVariables.EnforceSystemCertificate)
+}
+
+func (c *config) EnforceSystemCertificateWhitelist() []string {
+	return c.productVariables.EnforceSystemCertificateWhitelist
+}
+
 func stringSlice(s *[]string) []string {
 	if s != nil {
 		return *s