Allow dragging model library outputs onto existing nodes

[mcmonkey4eva]

for #1000

This also changes modelToNodeStore to be backed by a list, which allows multiple node type registrations - that way many different nodes can be registered as compatible with a given model class.

(Future todo: automatic registration from object_info maybe? We can easily identify which inputs have lists that exact match a given expected model type list, and arguably that can be abused to define compatibility. Or if not, maybe a field in the custom node in python side?)

Having the list that allows multiple entries also means we can in the future display a list of what node types are valid and let the user choose / set defaults / etc.

I've registered a second core loader node for checkpoint and lora, and validated that dragging onto either works. Naturally this also providers an easy test reference for other future usages of the multiple node options list.

Also added quickRegister to reduce the copypasta

[huchenlei]

Can you add a playwright test to verify this feature works?

[huchenlei]

You can use the new util functions to get node ref for node position now and avoid hardcoded node position calculation.

ComfyUI_frontend/browser_tests/ComfyPage.ts

Lines 878 to 897 in 2531ec1

	async getNodeRefById(id: NodeId) {
	return new NodeReference(id, this)
	}
	async getNodeRefsByType(type: string): Promise<NodeReference[]> {
	return (
	await this.page.evaluate((type) => {
	return window['app'].graph.nodes
	.filter((n) => n.type === type)
	.map((n) => n.id)
	}, type)
	).map((id: NodeId) => this.getNodeRefById(id))
	}
	async getFirstNodeRef(): Promise<NodeReference | null> {
	const id = await this.page.evaluate(() => {
	return window['app'].graph.nodes[0]?.id
	})
	if (!id) return null
	return this.getNodeRefById(id)
	}
	}

[huchenlei]

Followup-work: when dragging a model, highlight all nodes that can be dropped onto.