[BHV-14587]MoonPopup controls are not focusable when there is an active scroller below it

The commit is to provide translation to Poup in  Z-direction, so that It
won't interfere with the controls below it.
Enyo-DCO-1.1-Signed-off-by: Rajyavardhan P rajyavardhan.p@lge.com
BHV-14587-updated code

translateZ  value is changed from 2px to 1px
BHV-14587: Place transformZ value in a private property and add documentation in one location.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>
Merge pull request #1626 from enyojs/BHV-14587-rajyavardhan.p

[BHV-14587]MoonPopup controls are not focusable when there is an active ...

Reviewed-by: Aaron Tam (aaron.tam@lge.com)