Implement horizontal row layout for Pivot Grid. Improvements to header navigation.

[skrustev]

Closes #14270

Additional information (check all that apply):

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

Checklist:

• [ ] All relevant tags have been applied to this PR
• [ ] 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

[MayaKirova]

The following features do not work with the new horizontal mode ATM:

• Sorting via the headers - fixed here: https://github.com/IgniteUI/igniteui-angular/pull/14415
• Resizing of dimensions via the UI - fixed cdeb976de7dd249dee16b648ee04af5dd4353346
• Export to excel produces wrong structure. - logged as separate task: https://github.com/IgniteUI/igniteui-angular/issues/14470
• Collapsing one dimension hierarchy, affects the state of the second dimension hierarchy. They should expand/collapse individually and retain their states.