packages/ui-layout/src/mirrorPlacement.js
function mirrorHorizontalPlacement (placement, delimiter) {
  return executeMirrorFunction(placement, (first, second) => {
    return [first, second].map(value => {
      return (value === 'start' || value === 'end') ? mirror[value] : value
    })
  }, delimiter)
}
function mirrorHorizontalPlacement (placement, delimiter) {
  return executeMirrorFunction(placement, (first, second) => {
    return [first, second].map(value => {
      return (value === 'start' || value === 'end') ? mirror[value] : value
    })
  }, delimiter)
}
function mirrorHorizontalPlacement ( placement , delimiter ) { return executeMirrorFunction ( placement , ( first , second ) => { return [ first , second ] . map ( value => { return ( value === 'start' || value === 'end' ) ? mirror [ value ] : value } ) } , delimiter ) }
Given a string or array of one or two placement values, mirrors the placement
horizontally.

Examples
```js
mirrorHorizontalPlacement('top start') // input
['top', 'end'] // output

mirrorPlacement('top start', ' ') // input
'top end' //output
```

@param {string|Array} placement - a string of the form '<value> <value>' or array [<value>, <value>]
@param {string} delimiter - when provided, a value with which the result array will be joined
@returns {string|Array} - an array of values or, if the delimiter was supplied, a string of
delimiter separated values
Given a string or array of one or two placement values mirrors the placement horizontally .