Get rid of VoicingManager.mainWindowVoicingEnabledProperty

[zepumph]

While trying to consolidate voicing-control Properties into a more solid structure over in phetsims/joist#743, @jessegreenberg and I realized that we can get rid of the purposes of the mainWindow Property and instead of voicingVisible. This will need to wait until that feature is complete in #1300.

Once that is ready, we can toggle voicingVisible when turning sim voicing on/off in joist. On hold until that is complete.

[jessegreenberg]

I hope that work in #1300 will make mainWindowVoicingEnabledProperty unnecessary, lets come back to this issue once that issue is done and make sure there is nothing else to do here.

[jessegreenberg]

#1300 is ready, no longer on hold.

[jessegreenberg]

There is a TODO in FocusManager that I don't fully understand

    // TODO: perhaps remove once reading blocks are set up to listen instead to Node.canSpeakProperty (voicingVisible), https://github.com/phetsims/scenery/issues/1343
    voicingManager.voicingFullyEnabledProperty.link( enabled => {
      this.readingBlockHighlightsVisibleProperty.value = enabled;
    } );

EDIT: This can be moved out of FocusManager and into joist, but I don't think it can be removed entirely. We don't want to display reading block highlights at all when "Sim Voicing" is not enabled.

[jessegreenberg]

@zepumph and I reviewed this together and we are excited to remove mainWindowVoicingEnabledProperty, and also move Properties form SpeechSynthesisAnnouncer to joist like voicingFullyEnabledProperty and voicingFullyEnabledProperty.
Probably rename voicingFullyEnabledProperty to contentAndToolbarVoicingEnabledProperty so it is more clear.

The only Property that seemed challenging to move out of scenery was voicingManager.speechAllowedAndFullyEnabledProperty in its usage in ReadingBlock.ts. But we decided we can replace it with Voicing.canAnnounceProperty, because that Property indicates whether the ReadingBlock can announce and should receive input via voicingVisibleProperty. Hooray!

[jonathanolson]

Patched a memory leak above (related to this issue?), can you verify? It was leaking on every new Display.

[zepumph]

Looks great. Thanks! Did this cause trouble somewhere? I'm curious if there is a use case where we are creating that many Displays?

[jonathanolson]

Yes, a memory leak in Density (there are a number of 3d sims that create Displays often, since they need to contain, size and rasterize content and update the content's rasterization when needed).