Add missing suppressLocalAudioPlayback setting

[beaufortfrancois]

I've noticed suppressLocalAudioPlayback setting was missing in https://w3c.github.io/mediacapture-screen-share/#extensions-to-mediatracksettings while https://w3c.github.io/mediacapture-screen-share/#dfn-suppresslocalaudioplayback says:

As a setting, this value indicates whether or not the user agent is applying local audio playback suppression to the source.

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[eladalon1983]

Could you modify the text to indicate that the value reflects what the app applied, and not whether the browser complied? That is, consider two distinct tabs A and B capturing C. If A suppresses C's playback and B does not, then we should still return false for B's query; it must not be allowed to observe the existence of A and its capture, let alone its settings.

[beaufortfrancois]

@eladalon1983 I've addressed your feedback.

[beaufortfrancois]

The more I think about it, I wonder which purpose is served for this specific setting if web developers can already get the value from getConstraints(). Maybe we should simply remove this line from the current spec:

As a setting, this value indicates whether or not the user agent is applying local audio playback suppression to the source.

[beaufortfrancois]

Following comment, we may want to actually keep suppressLocalAudioPlayback in getSettings() though. @jan-ivar Can you review this PR?

[beaufortfrancois]

Thank you @jan-ivar! I've addressed your feedback.

[beaufortfrancois]

@eladalon1983 @jan-ivar Please merge

[eladalon1983]

The current work mode is that we merge PRs during a meeting on Thursday.

[jan-ivar]

Forgot this one this morning, and it's editorial, so merging.