Support default-permission in aconfig_declarations

Aconfig provides new argument, default-permission, for create-cache.
When buld aconfig_declarations, aconfig_declarations will read the value
from release configuration to pass this value to aconfig.

Bug: 294417368
Test: presubmit
Change-Id: Id55dab1d757e2366a62449c73e2497cc958c5e78
diff --git a/android/config.go b/android/config.go
index eb89493..0ef3b91 100644
--- a/android/config.go
+++ b/android/config.go
@@ -200,6 +200,12 @@
 	return c.config.productVariables.ReleaseAconfigValueSets
 }
 
+// The flag default permission value passed to aconfig
+// derived from RELEASE_ACONFIG_FLAG_DEFAULT_PERMISSION
+func (c Config) ReleaseAconfigFlagDefaultPermission() string {
+	return c.config.productVariables.ReleaseAconfigFlagDefaultPermission
+}
+
 // A DeviceConfig object represents the configuration for a particular device
 // being built. For now there will only be one of these, but in the future there
 // may be multiple devices being built.