Simplify UpgradableConstructor use of native lifecycle callbacks

[nolanlawson]

(This bug only applies to native custom element lifecycle mode.)

Currently the UpgradableConstructor uses a WeakMap to keep track of lifecycle callbacks for FACE:

lwc/packages/@lwc/engine-dom/src/custom-elements/create-custom-element.ts

Lines 45 to 48 in 187a24d

	instancesToFormAssociatedCallbacks.set(this, formAssociatedCallbackToUse!);
	instancesToFormDisabledCallbacks.set(this, formDisabledCallbackToUse!);
	instancesToFormResetCallbacks.set(this, formResetCallbackToUse!);
	instancesToFormStateRestoreCallbacks.set(this, formStateRestoreCallbackToUse!);

However, it doesn't do this for connected/disconnected callbacks:

lwc/packages/@lwc/engine-dom/src/custom-elements/create-custom-element.ts

Lines 97 to 111 in 187a24d

	if (hasConnectedCallback) {
	(UpgradableConstructor.prototype as any).connectedCallback = function () {
	if (!elementsUpgradedOutsideLWC.has(this)) {
	connectedCallback(this);
	}
	};
	}
	if (hasDisconnectedCallback) {
	(UpgradableConstructor.prototype as any).disconnectedCallback = function () {
	if (!elementsUpgradedOutsideLWC.has(this)) {
	disconnectedCallback(this);
	}
	};
	}

This is technically a bug, since the connected/disconnected callbacks effectively are created once per constructor and never change per instance. So you might think that the connected/disconnected callbacks should use the same WeakMap system as the FACE callbacks, in order to fix the bug.

However, it doesn't actually matter in practice, because every callback closure just passes in this/elm, which is unique per instance:

lwc/packages/@lwc/engine-core/src/framework/rendering.ts

Lines 340 to 357 in 187a24d

	connectedCallback = (elm: HTMLElement) => {
	connectRootElement(elm);
	};
	disconnectedCallback = (elm: HTMLElement) => {
	disconnectRootElement(elm);
	};
	formAssociatedCallback = (elm: HTMLElement) => {
	runFormAssociatedCallback(elm);
	};
	formDisabledCallback = (elm: HTMLElement) => {
	runFormDisabledCallback(elm);
	};
	formResetCallback = (elm: HTMLElement) => {
	runFormResetCallback(elm);
	};
	formStateRestoreCallback = (elm: HTMLElement) => {
	runFormStateRestoreCallback(elm);
	};

(To get the vm, the underlying callbacks call getAssociatedVM(elm).)

Here is a test that confirms that the current behavior is correct: 687572e

So basically, the WeakMaps are useless at best and a perf hit at worst. It should be possible to greatly simplify this code.