Intent to unship: mozPreservesPitch

[Ashley Zebrowski]

As per the HTML standard, preservesPitch should be used without a vendor prefix.

Link to standard for preservesPitch:
https://html.spec.whatwg.org/multipage/media.html#dom-media-preservespitch-dev

As an intermediary step before removing mozPreservePitch, the following bug marks it as deprecated, adds support for unprefixed preservesPitch, and updates tests accordingly:
https://bugzilla.mozilla.org/show_bug.cgi?id=1652950

The following bug has been filed to remove support for mozPreservePitch entirely once we have gathered sufficient usage data:
https://bugzilla.mozilla.org/show_bug.cgi?id=1765201

Status for unprefixed preservesPitch on other browsers is:
Full support: Chrome, Edge, Opera, WebView Android, Chrome Android, Opera Android, Samsung Internet
Requires vendor prefix to use: Safari, Safari on iOS, Firefox (currently)
No support: Internet Explorer

Best,
-AZ