VaDatePicker a11y

[Roman4437]

closes #3744

added essential roles and attributes

[m0ksem]

Please use format prop in aria-label.

Also, why did you skip role "presentation", "aria-live " and "aria-atomic"? We change grid using arrow buttons, so it must be applied here I think (Im not sure).

These changes also must be applied to months picker and something must be changed in year picker.

[m0ksem]

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.