[Meta] Split toolbar utility out of EuiDataGrid

[JasonStoltz]

Folks often use the EuiDataGrid purely for it's toolbar. Ideally, we could split out the toolbar into an independent utility of it's own.

<TODO: Examples would be great here>

This Meta issue is meant to aggregate a couple of different requests related to that into a single backlog item.

### Tasks
- [ ] https://github.com/elastic/eui/issues/3500
- [ ] https://github.com/elastic/eui/issues/4010