Add GetUserNameFromEmailAsync to IdentityUserManager.

[maliming]

No description provided.

[codecov]

Codecov Report

Attention: 89 lines in your changes are missing coverage. Please review.

Comparison is base (b9a6bff) 51.61% compared to head (3a23269) 51.60%.
Report is 50 commits behind head on rel-8.0.

Files	Patch %	Lines
...sts/Volo/Abp/Identity/IdentityUserManager_Tests.cs	0.00%	61 Missing ⚠️
...ty.Domain/Volo/Abp/Identity/IdentityUserManager.cs	75.00%	13 Missing and 9 partials ⚠️
...ing/Templates/RandomizeAuthServerPassPhraseStep.cs	0.00%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           rel-8.0   #18612      +/-   ##
===========================================
- Coverage    51.61%   51.60%   -0.02%     
===========================================
  Files         3074     3074              
  Lines        96942    97091     +149     
  Branches      7712     7729      +17     
===========================================
+ Hits         50040    50106      +66     
- Misses       45370    45444      +74     
- Partials      1532     1541       +9     

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