Pass previous_api for module lib stubs contributions

Currently, the previous_api property is set for the default modules
generated in the api.go used from from-text stubs generation, but
this was omitted for `android_module_lib_stubs_current_contributions`.
This change adds the missing property for this module.

Test: Patch https://r.android.com/3133694 && m HealthConnectToolbox
Change-Id: I8d3b1ebefb8108d3061413126aa7ec4da11e6164