Rearrange expression namespaces

[Tigrov]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	❌
Fixed issues

Related PRs

• Rearrange expression namespaces db-sqlite#391
• Rearrange expression namespaces db-mysql#428
• Rearrange expression namespaces db-pgsql#447
• Rearrange expression namespaces db-mssql#398
• Rearrange expression namespaces db-oracle#365
• Rearrange expression namespaces active-record#450

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.41%. Comparing base (c69110a) to head (0f8d8d8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1052   +/-   ##
=========================================
  Coverage     98.41%   98.41%           
  Complexity     1647     1647           
=========================================
  Files           115      115           
  Lines          4355     4355           
=========================================
  Hits           4286     4286           
  Misses           69       69           

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