minor improvements to `toEulerAnglesTo()` (#12588)
minor improvements to `toEulerAnglesTo()` (#12588)

Reuse `zAxisY` in avoid unnecessary math
Moved some constants inside of the branch where they are used
RaananW/Babylon.js,RaananW/Babylon.js,BabylonJS/Babylon.js,BabylonJS/Babylon.js,RaananW/Babylon.js,BabylonJS/Babylon.js,sebavan/Babylon.js,sebavan/Babylon.js,sebavan/Babylon.js