UtteranceQueue to be parameteric to the Type of its announcer

[zepumph]

@chrisklus and I found that it would be nice to have UtteranceQueue have a parametric typescript type that was the actual Announcer type. THis way the announcer Property would have the right type associated with it for access. This is valuable for some number suite cases where we pass through utterance queues and want to have access to particular announcer subtype methods.

[zepumph]

@chrisklus is this helpful for you? Now you can do something like new UtteranceQueue<NumberSuiteAnnouncer>.

[chrisklus]

Your commit looks great! This is working really nicely over in phetsims/number-suite-common#58. Thanks! Closing.