Add convenience Java API to froze Grid multiselect checkbox column

[TatuLund]

Describe your motivation

When there is lot of columns, it would be preferable to froze the checkbox column for easy toggling of the selection. The current API is too hard to find, hence convenience API in Grid would be desired.

((GridMultiSelectionModel<?>) grid
  .setSelectionMode(Grid.SelectionMode.MULTI))
  .setSelectionColumnFrozen(true);

Describe the solution you'd like

Naming proposals

grid.setSelectionColumnFrozen(true)

Describe alternatives you've considered

No response

[web-padawan]

There's actually an API for that but it's not on the Grid itself, see #1198 (comment)

[TatuLund]

@web-padawan thanks for noting that. I updated the ticket scope.

[tomivirkki]

Related:

• Frozen columns in grid with multiple selection #1198
• Grid with frozen column not working correctly when selectionMode is multi #5666