[EuiPopover] should default to ownFocus

[myasonik]

ownFocus={false} isn't really accessible in most situations so changing the default should be a good improvement

Is this considered a breaking change? I don't really think so practically but I think it is technically...

[cchaos]

It's not a breaking change because it doesn't require consumers to afford for the change.

[chandlerprall]

Re-opening this because the fix is being reverted for now, as the focus trap causes issues with popovers in Kibana's top navigation.

[myasonik]

Now that we're after the winter holidays, should we try this one more time?

[chandlerprall]

We def should, but it'll need to wait until after the datagrid virtualization & emotion theming unless you want to own it 😃