+ flatten specificity with `:where` selector

- JS logic lets us flatten and add more explanatory comments for the different height types

- fairly straightforward
- DRY out flex CSS between cell and focus trap div

- just inline it, it's only used once

- flatten left/right CSS since we have the prop right here

+ remove unnecessary flex-shrink CSS on the arrow - `EuiIcon` already takes care of that inherently

- just reuse EuiButtonIcon with transform/animations unset and remove `__icon` - simplifies a ton of CSS

- handle fontSize sizing of actions button in top level data grid styles

- use `:not()` CSS to handle hidden state instead, which simplifies even more CSS

+ convert inline Emotion to styles & fix line-height shenanigans

+ move complex selectors to new util

+ wrap transition in animation media query

- remove unnecessary `.euiDataGridHeaderCell__content` div element in control columns - it's not doing anything useful, so we might as well delete it

+ fix `focus_utils` rendering a `null` in control column `aria-describedby`

- font weight appears to be unused from an old theme

- let's replace it with actual english text instead that indicates what clicking the button will do

+ [enhancement] improve smoothness of dragging visibility with an `isDragging` modifier

- clean up unnecessary inline style (only useful when dragging, we don't need it during, e.g. snapshots)

+ convert enzyme tests to RTL (requires using a ref for class methods instead of `.instance()`)

…lbarVisibility` stories

- for some reason the ref was breaking the docgen??

- we didn't actually need the stateful grid for the ref tests, so just get rid of it

…ction component

- not sure how much performance this is gaining us (if at all, it might be losing?) so IMO this is primarily a dev readability enhancement

+ make a few more props not overrideable via `setCellProps` (& update types)

+ write tests for merged `setCellProps` props

- otherwise, it continuously reads out "and 3 more items" instead of the full SR text :/

- neither the SR text or the cell actions are dependent on the renderCellValue content, and they don't need to be parsed by `HandleInteractiveChildren`, so move them out to the parent EuiDataGridCell

+ clean up now-unnecessary waterfalled props

- move screen reader text out to its own function component to continue using useEuiI18n

cleaner snapshots, less DOM rendered, and and behaves the same way for screen readers, so why not

- aria-describedby text doesn't need to be visible at all, we can just use `hidden`, which removes it from the copy clipboard

+ condense down to a single element