feat(mat/select): add page down/up button functionality

[forsti0506]

Hello,

small PR on adding some functionality according to (https://github.com/angular/components/issues/3549) and implemented to fit the standard.

• Page-Down focuses the last element in the select
• Page-Up focus the first element in the select
• It's done in open and closed state (https://w3c.github.io/aria-practices/examples/combobox/combobox-select-only.html there it is only in closed state, but for example in Chrome a native select is working cloed and open this way)

Best regards,

Martin