Copy apex_available properties to snapshot modules

Bug: 142935992
Test: m nothing
Change-Id: I1cdaae5b4e13a89dc46541dacd34ef5a44735b6a
diff --git a/android/apex.go b/android/apex.go
index 43a42df..026d685 100644
--- a/android/apex.go
+++ b/android/apex.go
@@ -116,6 +116,10 @@
 	return m
 }
 
+func (m *ApexModuleBase) ApexAvailable() []string {
+	return m.ApexProperties.Apex_available
+}
+
 func (m *ApexModuleBase) BuildForApexes(apexes []ApexInfo) {
 	m.apexVariationsLock.Lock()
 	defer m.apexVariationsLock.Unlock()