Match the declarations to GNOME Shell 51

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GNOME 51 moved event handling off actor vfuncs and onto Clutter actions, gestures and key binding pools. The shell classes stopped overriding vfunc_*_event and grew signal handlers instead. Those vfuncs still exist on Clutter.Actor, so nothing fails to compile. The declarations just stopped describing the shell, quietly.

Stacked on #145, which is stacked on #144. Merge those first and this diff is only the two commits below.

First commit, sync with 51

Checked module by module against gnome-shell at tag 51.beta, for every declared name that changed between 50.4 and 51.beta.

module	what changed
appDisplay	BaseAppView / AppDisplay._onScroll now takes the ScrollController::scroll arguments, and _onKeyPressEvent became a binding pool closure
boxpointer	_muteKeys is a Clutter.KeyController and _muteInput a Clutter.ClickGesture, both were boolean
calendar	vfunc_scroll_event became _onScroll
dialog	vfunc_event became a KeyController
layout	HotCorner.vfunc_leave_event is gone
messageList	URLHighlighter motion and leave became a MotionController, Message.vfunc_key_press_event became _closeIfAllowed
messageTray	_onNotificationKeyRelease became a binding pool closure
modalDialog	vfunc_captured_event is gone
search	new exported SearchEntry, with its activate-new-instance signal
slider	scroll and key vfuncs became _onScroll, _moveLeft, _moveRight
status/backlight	SliderItem forwards vfunc_navigate_focus to the slider
status/volume	_handleScrollEvent became _onScroll plus _handleScroll
switcherPopup	key and scroll vfuncs became _onKeyPress, _onModifierChange, _onScroll
userWidget	new showAvatar and hideAvatar

Everything added carries @version 51, per the convention. I applied it to the handlers whose arguments 51 reshaped as well, appDisplay._onScroll for one, since the declared contract is the 51 one. Trim those if you read the tag more strictly.

Two additions I left out, because those classes declare no members at all and one more private helper would not help anyone. ActivitiesButton._toggleAction in panel, declared as class ActivitiesButton extends Button {}, and WindowPreview._onEnter / _onLeave in windowPreview, which declares exactly two members.

Second commit, names 51 did not remove but an earlier release did

Checking those modules turned up a second group, absent at 50.4 as well. They describe an API no supported shell has. Same files, so the same PR, but a separate commit, because it is a different claim and you may want to judge it separately.

slider is the worst of them. startDragging, _endDragging, _motionEvent, scroll and three vfuncs all went away when the pan gesture landed, and step(nSteps), the method status/volume actually calls, was never declared. That one I added. It predates 51, so it carries no @version tag.

What is still wrong after this PR

The same check across the whole package still reports 37 stale member declarations in 12 files. All of them are in modules GNOME 51 did not touch, so they are outside this PR's scope, but they are the same defect.

• misc/systemActions: _loginManager
• ui/animation: _animationsLoaded, _init, _loadFile, _onDestroy, _showFrame, _syncAnimationSize, _update
• ui/closeDialog: _onFocusChanged, _tracked
• ui/components: _sessionUpdated
• ui/dnd: _dragState, _eventIsRelease, _grabActor, _grabDevice, _maybeStartDrag, _onButtonPress, _onTouchEvent, _ungrabActor, _ungrabDevice
• ui/iconGrid: _childAdded, _childRemoved
• ui/messageList: _closeButton, _getIcon, _onUpdated, _secondaryBin
• ui/status/accessibility: _buildItemExtended
• ui/status/brightness: _changeSlider, _proxy, _sliderChanged, _sliderChangedId
• ui/status/network: _closeConnectivityCheck, _flushConnectivityQueue, _portalHelperDone
• ui/status/remoteAccess: vfunc_event
• ui/status/thunderbolt: _ensureSource, _source

ui/animation is the striking one. Spinner uses a constructor now, and the Animation base class the declaration describes is not in js/ui/animation.js at all any more.

There is a stale export too. search.d.ts exports MaxWidthBox, which upstream has kept module-private since at least 50.4. Removing an export breaks consumers, so I left it alone.

The part worth automating

I found all of this with a throwaway script. Parse the declared members out of each .d.ts, parse the defined names out of the matching js/ file at a given tag, print the difference. It found the 51 drift and the older drift in one run, and it is the only reason this PR is a list rather than a guess.

It could live in the repo as scripts/check-shell-api.mjs, run against a shallow git clone --depth 1 --branch <tag> of gnome-shell, so each cycle starts from a diff instead of from whatever the compiler happens to notice. It cannot be a required check until the 37 above are dealt with, but it can run and report. Say the word and I will send it.

One caveat, so nobody over-trusts it. It matches names, not shapes. It cannot see a method whose signature changed, and it has false positives around static class fields. _mediaSource in messageList was one, a static _mediaSource = …, which I checked and kept. Every removal in this PR I verified by reading the upstream source, not by trusting the script.

Validation

build:types, prettier:check, validate:types, build:example and validate:example all pass locally.