Start widgetmanager in PZP isolate on Android

Jira issue: WP-934

This starts the widgetmanager, but initialises the Android-side binding
in the PZP isolate, and suppresses the initialisation in a separate
isolate.
Separate require of open and widgetmanager to ensure failures are independent.

Jira issue: WP-934
Reinstate setting up some widgetmanager state.

Jira issue WP-934
Start AppLauncher module after WidgetManager

Jira issue: WP-934
Create WidgetManagerService to hold WidgetManagerImpl and associated
listener state.

Jira issue: WP-934
Merge pull request #571 from paddybyers/android-inprocess-wgtmgr3

Move widgetmanager to PZP isolate on Android