Multi Row Layout keyboard navigation

[dkamburov]

Closes #4708
Related #4384

TODO:

• Automate scenarios with Tab navigation, including cell, row editing, and navigating with Ctrl
• Fix Ctrl + Up/Down navigation
• Fix navigation from pinned or unpinned area

Additional information (check all that apply):

• Bug fix
• 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
• This PR includes API docs for newly added methods/properties
• 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
• This PR includes behavioral changes and the feature specification has been updated with them

[MayaKirova]

@PavlovVasil Please re-test with latest changes.

[PavlovVasil]

@dkamburov @ChronosSF @MayaKirova @mpavlinov
The issue with "Tab" key not scrolling horizontally has been fixed. There are two more:

1. When a cell from a pinned group gets focused, the bottom-border of the cells disappears. Running the samples repo and opening http://localhost:4200/samples/grid/grid-multi-row-layout would show you this if you select a cell in the first row:

The dev demos look like this if you click the button and pin the "Pin/Unpin Second Group" button at the bottom:

2. If Group By has been enabled:
   1. Run the samples repo and open http://localhost:4200/samples/grid/grid-multi-row-layout
   2. Collapse all groups by clicking the button at the top left
   3. Expand the first three groups as well as the last one
   4. Click the middle cell of the last grid row - "London"
   5. Hold the up arrow key in order to scroll to the top
      Result:
      When the navigation tries to scroll through the collapsed groups, it looses focus and stops working. The scroll position is not correct either, and scrolls to the bottom:

[MayaKirova]

@PavlovVasil Regarding 1). It is not an issue related to navigation, same can be reproduced in master if you select a cell range in MRL grid. Seems to be a styling issue due to an additional style that applies border-bottom: 0. Please log it separately.

[MayaKirova]

@PavlovVasil Please re-test.