fix(pivot-grid): added createRow method for grid based events

[tishko0]

Closes #14970

Additional information (check all that apply):

• [x] Bug fix
• [ ] New functionality
• [ ] Documentation
• [ ] Demos
• [ ] CI/CD

Checklist:

• [ ] All relevant tags have been applied to this PR
• [x] This PR includes unit tests covering all the new code (test guidelines)
• [ ] This PR includes API docs for newly added methods/properties (api docs guidelines)
• [ ] This PR includes feature/README.MD updates for the feature docs
• [ ] This PR includes general feature table updates in the root README.MD
• [ ] This PR includes CHANGELOG.MD updates for newly added functionality
• [ ] This PR contains breaking changes
• [ ] This PR includes ng update migrations for the breaking changes (migrations guidelines)
• [ ] This PR includes behavioral changes and the feature specification has been updated with them

[skrustev]

I assume you have checked that all methods are working correctly.

1. I have suspicion that the selected getter/setter might not work judging by how it is implemented in the IgxPivotRow, so make sure they work along with everything in the IgxPivotGridRow

2. The key for a single pivot row also is a bit of a weird concept now that I think about it. Also doesn't seem to be close to how it is implemented in the Pivot Grid. Might be better to return the full key for a row. That would mean getting the record key by the last row dimension and the selection would check if the selected key in the selection service is a subset of that pivot row key.