refactor: Move linked chunk into matrix-sdk-common and few event cache types into matrix-sdk-base

[Hywan]

In order to implement the event cache persistent storage for events, we need some types from matrix_sdk::event_cache inside matrix_sdk_base, and we need linked_chunk inside matrix_sdk_common.

First off, this patch renames matrix-sdk-base/src/event_cache_store to matrix-sdk-base/src/event_cache/store. Second, it moves linked_chunk inside matrix-sdk-common. And lastly, it moves 2 event cache types into matrix-sdk-base.

That's it folks.

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• Address [meta] EventCache storage #3280

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.93%. Comparing base (403be3d) to head (181eb62).
Report is 24 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4247   +/-   ##
=======================================
  Coverage   84.93%   84.93%           
=======================================
  Files         274      274           
  Lines       29726    29728    +2     
=======================================
+ Hits        25247    25249    +2     
  Misses       4479     4479           

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