Support "ctrl + a" for non async select

[kikonen]

For non async select, could support ctrl+a. For async (remote) select this clearly not really feasible.

From uset perspective, however, if there is typehead field then this would conflict with it.

References
https://www.w3.org/TR/wai-aria-practices/#Listbox

[kikonen]

#88 covers use cases for this pretty well