VaGrid component

[m0ksem]

Let's have a component that allow user to build components that behaves as grid. We will use it later in DatePicker.

Usage example:

We can take existing code from VaDatePicker.

• We need: VaGrid, VaGridRow, VaGridCell components.
• VaGrid must have focusable prop and isFocused in slot <VaGridCell focusable="boolean" #default="{ isFocused }" />
• Keyboard navigation must be implemented with Arrows.
• Aria roles must be applied.

Please, connect in Discord before implementation!

I checked out that gridcell must be used in row. It is a requirement, otherwise gridcell will not be recognized. We're using css grid here, so we don't have an actual row element... 

I think we need to change component layout from css grid, to more general approach with row

roles:
```
grid
  row
     columnheader <- weekdays
  rowgroup
     row
       gridcell <- date
 ```
 
What if we make VaGrid component, which will implement all of these with keyboard navigation? I think it might be useful for people who make something like cinema chair picker or whatever requires navigation with grid. We could reuse VaGrid in DatePicker. I think for this PR we can simply remove wrong roles and implement VaGrid component later.

Originally posted by @m0ksem in #3747 (comment)