Enable ManageMediaSource by default on iPhone

https://bugs.webkit.org/show_bug.cgi?id=260692
rdar://114270414

Reviewed by Youenn Fablet.

Enabled on all cocoa platforms where ENABLE_MEDIA_SOURCE is defined.

* Source/WebKit/Shared/WebPreferencesDefaultValues.cpp:
(WebKit::defaultManagedMediaSourceEnabled):

Canonical link: https://commits.webkit.org/267273@main

Source/WebKit/Shared/WebPreferencesDefaultValues.cpp

@@ -178,10 +178,7 @@ bool defaultManageCaptureStatusBarInGPUProcessEnabled()
 #if ENABLE(MANAGED_MEDIA_SOURCE) && ENABLE(MEDIA_SOURCE)
 bool defaultManagedMediaSourceEnabled()
 {
-#if PLATFORM(IOS_FAMILY)
-    // Enable everywhere that MediaSource is enabled
-    return defaultMediaSourceEnabled();
-#elif PLATFORM(MAC)
+#if PLATFORM(COCOA)
     return true;
 #else
     return false;