Reintroduce EuiSwitch a11y changes

[thompsongl]

#2193 was reverted because of difficulty upgrading Kibana. We want to reintroduce the changes and ensure time for upgrading Kibana before a FF

[thompsongl]

Design question (@snide): elastic/kibana#43717 (comment)
Gist: Switches without labels are no longer valid. Is this ok? If so, we'll need to audit usage and decide what to do with label-less switches in Kibana.

[snide]

@thompsongl Lookign at the changes there, if switches are buttons, an aria-label should be ok in place of the label. Specifically that linked case is a good example of one (it looks like an aria-label is on it as well)

[thompsongl]

Ok. I think we'll just need to update EuiSwitch to require either a label or and aria-label (right now I think a label is required)

[thompsongl]

Functional test updates are the other sizeable effort. The original PR (linked above) has a lot of work we can cherry pick, but not every failure was resolved.

[myasonik]

What sort of situations are we getting into where we have switches without labels? Know of any examples?

(Dave's right, we can technically support it with aria-label but it just sounds like I'd need to know what a control is before I click on it...)

[thompsongl]

@myasonik elastic/kibana#43717 (comment) shows one case. It's likely there are others, but we'd have to find them.

[snide]

There are always going to be plenty. The label will often not be phsyicially bound to the component, but be described elsewhere. The very common example is anytime we need to show a column of switches against rich content.

[thompsongl]

Refreshed my memory of just why this was so hard the first time around: Angular.

We'll have to find a shim/manual update of Angular form dirty/touched checking for instances of EuiSwitch in Vis (still uses quite a lot of Angular). Per elastic/kibana#38269, we likely can't just wait for Angular to be removed. Just an update on the way forward.

[myasonik]

Would we ever ship 2 versions of a component?

Like a AngularDeprecatedEuiSwitch and EuiSwitch...

[snide]

Would we ever ship 2 versions of a component?

I'd try to avoid doing this. It creates a matrix of maintainability on both sides that gets hairy. The last thing we want to do is make the situation more complicated to understand.