Bug 1528042 - Limit enumerateDevices() fingerprinting vector ahead of…

… (and after) getUserMedia success, to spec. r=karlt

Updates enumerateDevices() to limit exposure of privacy sensitive
information ahead of actual camera or microphone use.

It also implements the "creating a device info object" algorithm correctly
after getUserMedia success, which only exposes information on cameras or
microphones (but not both) if only one or the other kind has successfully
been used.

Includes the latest privacy improvements to the spec:
- w3c/mediacapture-main#632
- w3c/mediacapture-main#641
- w3c/mediacapture-main#773

This also fixes media.navigator.permission.disabled leaking labels.

Differential Revision: https://phabricator.services.mozilla.com/D100378

UltraBlame original commit: 55c6b85b37c1fb8d6d0b6a273e237b4921672743