[Cocoa] Upgrade ManagedMediaSource status to preview

[jernoble]

09dcc94

[Cocoa] Upgrade ManagedMediaSource status to preview
https://bugs.webkit.org/show_bug.cgi?id=255241
rdar://105992988

Reviewed by Eric Carlson.

Enable in all the same places as MediaSource.

* Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml:
* Source/WebKit/Shared/WebPreferencesDefaultValues.cpp:
(WebKit::defaultManagedMediaSourceEnabled):

Canonical link: https://commits.webkit.org/262805@main

0e948ce

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
✅ 🛠 🧪 jsc	✅ 🛠 tv	✅ 🧪 api-ios	❌ 🧪 api-gtk
✅ 🛠 🧪 jsc-arm64	✅ 🧪 mac-wk2	✅ 🧪 mac-AS-debug-wk2	✅ 🛠 jsc-armv7
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2-stress	✅ 🧪 jsc-armv7-tests
✅ 🛠 🧪 merge	✅ 🛠 watch		✅ 🛠 jsc-mips
	✅ 🛠 watch-sim		✅ 🧪 jsc-mips-tests

[webkit-early-warning-system]

EWS run on current version of this PR (hash 0e948ce)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🛠 gtk
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🧪 gtk-wk2
✅ 🛠 🧪 jsc	✅ 🛠 tv	✅ 🧪 api-ios	❌ 🧪 api-gtk
✅ 🛠 🧪 jsc-arm64	✅ 🧪 mac-wk2	✅ 🧪 mac-AS-debug-wk2	✅ 🛠 jsc-armv7
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2-stress	✅ 🧪 jsc-armv7-tests
✅ 🛠 🧪 merge	✅ 🛠 watch		✅ 🛠 jsc-mips
	✅ 🛠 watch-sim		✅ 🧪 jsc-mips-tests

[webkit-commit-queue]

Committed 262805@main (09dcc94): https://commits.webkit.org/262805@main

Reviewed commits have been landed. Closing PR #12582 and removing active labels.