Keep 'partition' in PackagingSpec

Add a property 'partition' to PackagingSpec and fill it when
PackagingSpec is created.

This will enable PackageModule to filter PackgingSpec based on
partition. (Will be used in a follow-up change)

Bug: 225121718
Test: m (nothing changes)
Change-Id: I7657edd380e215df66bae57d8b07dd4181841fdf
diff --git a/android/packaging.go b/android/packaging.go
index e3a0b54..e5a7fa4 100644
--- a/android/packaging.go
+++ b/android/packaging.go
@@ -40,6 +40,8 @@
 	executable bool
 
 	effectiveLicenseFiles *Paths
+
+	partition string
 }
 
 // Get file name of installed package
@@ -67,6 +69,10 @@
 	return *p.effectiveLicenseFiles
 }
 
+func (p *PackagingSpec) Partition() string {
+	return p.partition
+}
+
 type PackageModule interface {
 	Module
 	packagingBase() *PackagingBase