Feature request: Expose open and close functions

[alexisjamet]

It should be very useful to use defineExpose in order to expose the close and open functions.

Then we could be able to open or close a popper from somewhere else in the page, something like:

## script
const foo = ref()
const openFoo = () => foo.value?.open()

## Template
<Popper ref="foo">blablabla</Popper>

<button @click="openFoo">I can open the popper Foo</button>

[bahung1221]

+1 same here

[luizhenriquerdias]

#75