While the expansion popover was originally built purely to be a full view of the cell contents, there is a growing need to make it more complex/custom. Several things that are needed:

• Allow consumers to control the open/closed state [Security Solution]Able to view Hit Enter modal and Inspect icon modal at same time after existing inspect full screen kibana#115339 (resolved by [EuiDataGrid] Allow consuming applications to control various internal state via ref #5590)
• Allow consumers to completely control the popover contents including the custom controls (resolved by [EuiDataGrid] Replace popoverContents API with renderCellPopover #5640)
• Fix the hard-coded high z-index (resolved by [EuiDataGrid] Fix cell popovers overlapping with modals and flyouts #5461)