Extract sync framework interaction to separate class

[sunkup]

Purpose

This is part of moving further away from the Sync Adapter Framework, which has been mostly replaced by Work Manager and is only used for sync requests coming from 3rd party apps and content changes.

While SyncAdapterServices is the entry point for said sync requests we are still en-/disabling general sync-ability and content triggered syncs for the sync framework via ContentResolver calls. These calls should be made from a single central place.

If we would ever like to change the notification of changed content provider entries to JobScheduler / WorkManager (https://github.com/bitfireAT/davx5/issues/247), it will be possible by adapting mainly this class and SyncAdapterServices.

Short description

• Create SyncFrameworkIntegration class with all necessary methods.
• Use it everywhere ContentResolver calls are made, except in the migrations

Note that due to the Android 7 contacts upload work-around there are still several places where ContentResolver.SYNC_EXTRAS_UPLOAD is in use.

Checklist

• The PR has a proper title, description and label.
• I have self-reviewed the PR.
• I have added documentation to complex functions and functions that can be used by other modules.
• I have added reasonable tests or consciously decided to not add tests.

[ArnyminerZ]

Just some small things, otherwise looks good 😄

[ArnyminerZ]

Looks good

[rfc2822]

Looks very good and I think it's a good starting point for possible improvements in the future. For instance now setIsSycnable and setSyncOnContentChange must be both called and you have to know that. In a future version it's maybe possible that we call methods more "blackbox" style without knowing such details. But this shouldn't be done in this PR.