[ic-time-selector] Add pageup/down functionality

### Summary
Add a pageup/down listener that increases/decreases the selection in the focused column by 10.

### 💰 Use value
It's a standard keyboard interaction behaviour that will make it significantly easier for keyboard-only users to change their selection using arrow keys.

10 is a bit of a magic number. It's a consistent recommendation from W3C but using 10 specifically isn't required. If a different number seems more suitable during testing, the developer should feel free to use a different number.

Start by locating the ic-time-selector component and its existing keyboard handling for the focused column and arrow keys. Implement and verify PageUp/PageDown selection changes, with the focused column moving by the chosen increment and keyboard-only interaction working as described.

Written by the indexing model from the issue text.