[iOS] Refactor some logic around VideoFullscreenInterfaceAVKit

[whsieh]

5771692

[iOS] Refactor some logic around `VideoFullscreenInterfaceAVKit`
https://bugs.webkit.org/show_bug.cgi?id=241113

Reviewed by Eric Carlson.

Adjust the window level of `VideoFullscreenInterfaceAVKit`'s window. No change in behavior.

* Source/WebCore/platform/ios/VideoFullscreenInterfaceAVKit.mm:
(VideoFullscreenInterfaceAVKit::doSetup):
* Source/WebKit/UIProcess/PageClient.h:
* Source/WebKit/UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::didEnterFullscreen):
(WebKit::WebPageProxy::didExitFullscreen):

Also refactor `WebPageProxy::did(Enter|Exit)Fullscreen`, such that we implement
`didExitFullscreen(PlaybackSessionContextIdentifier)` in the case where
`ENABLE(VIDEO_PRESENTATION_MODE)` is enabled, and `didExitFullscreen()` (with no arguments) in the
case where it's disabled.

Currently both versions of `did(Enter|Exit)Fullscreen()` exist if `ENABLE(VIDEO_PRESENTATION_MODE)`
is set, even though we only expect to call into `did(Enter|Exit)Fullscreen()` from outside of
`WebPageProxy`.

* Source/WebKit/UIProcess/WebPageProxy.h:
* Source/WebKit/UIProcess/ios/PageClientImplIOS.h:
* Source/WebKit/UIProcess/ios/PageClientImplIOS.mm:
(WebKit::PageClientImpl::didEnterFullscreen):
(WebKit::PageClientImpl::didExitFullscreen):
* Source/WebKit/UIProcess/ios/WKContentViewInteraction.h:
* Source/WebKit/UIProcess/ios/WKContentViewInteraction.mm:
(-[WKContentView _didEnterFullscreen]):
(-[WKContentView _didExitFullscreen]):
* Source/WebKit/UIProcess/mac/PageClientImplMac.h:

Canonical link: https://commits.webkit.org/251147@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@295052 268f45cc-cd09-0410-ab3c-d52691b4dbfc

[whsieh]

Thanks for the review!

[webkit-early-warning-system]

Committed r295052 (251147@main): https://commits.webkit.org/251147@main

Reviewed commits have been landed. Closing PR #1168 and removing active labels.