fix(material/list): fix action-list focus state for high contrast firefox (#23584)
fix(material/list): fix action-list focus state for high contrast firefox (#23584)

Fixes the focus state on the action-list for firefox in high-contrast
mode. In firefox, the outline only renders on the top, right and left –
not the bottom. This fixes the bottom of the outline being cut-off by
setting the z-index of the focused list item to 1.

fixes #23583
crisbeto/material2,josephperrott/material2,crisbeto/material2,josephperrott/material2,crisbeto/material2,josephperrott/material2,josephperrott/material2,angular/components,crisbeto/material2,angular/components,josephperrott/material2,angular/components,angular/components