[WIP] Type-to-Search, plus toolbar a11y changes

[schanzer]

1. User enters edit mode
2. As they type, the text of the node is entered as the search text in the primitive list
3. As the list changes, an aria-live region announces the number of primitives
4. Up/Down Arrow searches the list
5. Enter inserts the identifier (followed by a space) in the editable node, keeping the user in edit mode and the cursor after the space
6. Space inserts the whole block, and leaves edit mode