Realize Schema::loadResultColumn() method

[Tigrov]

Related PR

• https://github.com/yiisoft/db/pull/945

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.88%. Comparing base (a7b35b1) to head (e619069). Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #397   +/-   ##
=========================================
  Coverage     99.88%   99.88%           
- Complexity      274      287   +13     
=========================================
  Files            33       33           
  Lines           844      890   +46     
=========================================
+ Hits            843      889   +46     
  Misses            1        1           

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

:rocket: New features to boost your workflow:

• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.