DataGrid should allow reordering columns without hiding

[myasonik]

Currently, there's one popover that handles reordering columns and show/hiding them.

In Discover, showing and hiding columns is handled outside of the grid so I don't want duplicate controls for that but I do still want to allow users to reorder columns.

This also calls into question whether the popover trigger name should be "hide fields". It's not clear to a user wanting to reorder columns that this is where they should go look and it becomes really confusing if we simply allow disabling the ability to hide fields.

[myasonik]

This is needed for Discover's DataGrid reimplementation (elastic/kibana#51531)