NavigationList (#1905)

* here we go!

* nav list

* divider

* collapsible

* here lies breaking changes

* item simplification

* update examples

* move to patterns

* tree view looks broken but its not

* remove notes

* stash

* action list component stories

* fix sub item

* revert treeview to original markup

* tree view readme

* story chaining

* cleanup + readme

* lint

* tree story fix

* Create quiet-walls-walk.md

* address feedback

Author: langermank

.changeset/quiet-walls-walk.md

@@ -0,0 +1,5 @@
+---
+"@primer/css": minor
+---
+
+Refactors NavigationList to better handle accessibility. Backwards compatible for TreeView CSS.