Generalize syncer

[sunkup]

Purpose

The sync algorithm of the different syncer implementations is very similiar. One generalized sync algorithm in the abstract syncer, with implementation details in the implemented Syncers, is less error prone and easier to understand and test with unit tests.

Future error handling (#887) should become easier as well.

Short description

• Passes only tasks authorities along, since the others can be inferred from chosen concrete syncer in BaseSyncWorker
• Acquires generic content provider in abstract syncer and specific TaskProvider in TaskSyncer
• Generalizes sync algorithm for the different resources (calendars, tasks, jtx collections, address books)
  • Provide collection to SyncManager #881 divided the process into four generic steps in every concrete syncer (CalendarSyncer, TasksSyncer, ...)
  • Now merges these steps in the abstract syncer and
    • calls abstract syncer methods implemented in extending syncers for the specific syncers resource details (i.e. create/delete/update a resource)
• use repositories instead of DAOs
• use new way to acquire logger
• drop SyncerTest - Tests will be added in seperate PR
• remove obsolete undocumented conditional (see 4e67988)
• NOTE: TaskSyncer still needs to acquire its own TaskProvider, since finding the local sync enabled collections with DmfsTaskList.find() requires it, which would in turn require some more rewriting in ical4android.

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.

Depends on #909

[github-actions]

This PR/issue depends on:

• Syncer synchronizes only once #909

[rfc2822]

Please rebase/merge from main-ose, changed a lot of things (mainly DI) that also affect Syncer constructors etc (but not its algorithm).

[sunkup]

@rfc2822 Ready :)

I used a nullable string for the url property of LocalCollection, since JtxCollection requires it. We could make the change in ical4android of course, but I felt it was not really worth it, if we are going to change to the ID property soon anyways.

Also the TaskSyncer still needs to acquire TaskProvider, see the PR description for details.

[rfc2822]

Looks already good with having the delete and url in the LocalCollection!

Did a few minor changes, and have some requests again.

[rfc2822]

I have created bitfireAT/ical4android#161 for future improvement :)

[rfc2822]

Looks very good now! Hope that everything will work as expected.