Add support for doctrine/orm 3

[Firehed]

Like doctrine/orm itself, this does include a major BC break: the default driver has moved from annotations to attributes, as the former has been removed.

[codecov]

Codecov Report

❌ Patch coverage is 21.66667% with 47 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.82%. Comparing base (6f82808) to head (f6f7213).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/InMemoryEntityManager.php	10.63%	42 Missing ⚠️
src/ArrayALC.php	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #43      +/-   ##
============================================
- Coverage     65.48%   64.82%   -0.67%     
+ Complexity      132      130       -2     
============================================
  Files             5        6       +1     
  Lines           310      307       -3     
============================================
- Hits            203      199       -4     
- Misses          107      108       +1     

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