Can canAnnounceProperties be TReadOnlyProperty?

[jessegreenberg]

In phetsims/friction#314 I wasn't allowed to do this

    const contextResponseUtterance = new Utterance( {
      priority: Utterance.MEDIUM_PRIORITY,
      voicingCanAnnounceProperties: [ voicingManager.voicingFullyEnabledProperty ]
    } );

because voicingFullyEnabledProperty is a TReadOnlyProperty and the canAnnounceProperty API require TProperty, Using a TReadOnlyProperty works and it doesn't look like the Properties of canAnnounceProperties need to be settable. Id like to broaden the API.

[jessegreenberg]

I went ahead in the above commit, @zepumph are you OK with this?

[zepumph]

Yes very good and very smart. Thanks.

[jessegreenberg]

Thanks!