- split out shared props, into main `Item` props - easier to follow combined at point as the `items` array prop

- have the accordion, group, and link components use `Pick` instead of `Omit` (see above about divergence)

NOTE: I played around with an ExclusiveUnion but I find the TS errors too annoying to understand how to fix - I'd rather degrade gracefully than annoy devs with hard to debug TS errors

- the whole accordion trigger should now toggle the accordion - no separate links

… props to accordion or link components

+ add missing test for `EuiCollapsibleNavGroup` - I forgot to write this before 😬

- not an a11y concern here, but it's more consistent UX wise

+ add missed `isCollapsible` spread to button component

- remove `href` links from accordions

- update `EuiCollapsibleNavItem edge` case story book more permutations

…or group/accordion' props

- means that the `items` prop shouldn't be passed at all if `href` is

…r/types