[Canvas] Embeddable z-indexes broken in Chromium 94

[crob611]

Several users have brought up that after upgrading to Chrome 94 or Edge 94 that embeddables on a workpad are unable to be moved or interacted with.

It appears there was a change in Chromium around the transform-style css property. https://chromestatus.com/feature/5640541339385856

This property is used by our element wrappers. Turning this style back to flat appears to fix the issue.

We should make sure this flat property does not cause any further issues and if not, backport the fix to previous releases, as this will likely be broken for every previous release.

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[Salmani]

Thanks @crob611 based on your comment I applied the following workaround for css as a global css override to our canvas workpads and it seems to have fixed the issue

.canvasPositionable{
  transform-style: flat;
}

[crob611]

Thanks @Salmani

Setting that CSS on the workpad is the current workaround for this issue. We will investigate to make sure that rule does not cause any further issues and then get that released in a future patch.