Make sdkMemberDependencyTag usable outside sdk package

Moves the struct to android/sdk.go and abstracts it behind a factory
method and interface. That allows it to be used outside the sdk
package.

This change is in preparation for adding support for module types that
have transitive sdk members.

Bug: 142940300
Test: m nothing
Change-Id: I71e5e0adf839b28a3a0952f82637637887f02688