feat(select): a11y focus on child options

[tjlav5]

Bug:

Focus of child options of an md-select is misrepresented by ChromeVox.

What is the expected behavior?

Keyboard navigation to a child option should set focus of ChromeVox to the location of the option in the menu.

What is the current behavior?

Keyboard navigation to a child option that overflows past the menu sets the focus of ChromeVox to the overflowed-location.

Note the orange box

What are the steps to reproduce?

1. Visit: https://material.angular.io/components/select/overview#creating-groups-of-options
2. Enable ChromeVox (likely reproducible in other OS/Screen-Readers too)
3. Keyboard navigate to Pokemon "Mew" (typing M-e-w)

What is the use-case or motivation for changing an existing behavior?

Screen readers should be treated as a first-class citizen with regards to product excellence.

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Angular 5.2.3
Chrome OS (ChromeVox) 64.0.3282.167

Anything else we should know?

Likely related to any fix of #1670

[jelbourn]

This is working as intended; the select uses aria-activedescendant instead of moving browser focus.

When you say ChromeVox, do you mean the Chrome Extension or the screen-reader in ChromeOS? If the former, it is explicitly not supported because it is not meant to be a real user-centric screen-reader.

[jelbourn]

Tracking via #11083

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