Slow hover performance regardless of list length

[mryellow]

• Vue Version: 2.6.11
• Vue Select Version: 3.20.4

Describe the bug

As described in #1013 @mouseover makes an assignment to typeAheadPointer.

This is then causing an update. This update is applying to all items within li as it counts as an update associated with that key.

This update causes any rich content sourced from components placed in the option slot to also suffer an update. This can't be overridden with subsequent key bindings as everything is a child of the li being touched.

Steps To Reproduce

• Install Vue Devtools.
• Enable "Highlight Updates"
• Mouseover list items
• Observe update spam

Expected behavior

• Should only update contents of option slot when data within option variable actually changes

[mryellow]

<template #option="option">
	<child-component
		:foo="option"
	/>
</template>

If child-component has a computed or uses the object in a template it will suffer an update.

<template #option="option">
	<child-component
		:foo="options.find(d => getOptionKey(d) === getOptionKey(option)"
	/>
</template>

Now after looking up the original option from the array rather than relying on the one passed through, no updates are suffered.

It's possible this has something to do with v-bind behaviour with slots. Struggled to nail it down exactly but do have a work-around. Could be that <slot :foo="bar"> behaves differently to <slot v-bind="{ foo: 'bar' }"> though have not confirmed.