Improve performance of ir.Utils.escapeJS.
Improve performance of ir.Utils.escapeJS.

gzm0/scala-js,andreaTP/scala-js,spaced/scala-js,lrytz/scala-js,sjrd/scala-js,scala-js/scala-js,japgolly/scala-js,andreaTP/scala-js,ummels/scala-js,jasonchaffee/scala-js,sjrd/scala-js,andreaTP/scala-js,scala-js/scala-js,SebsLittleHelpers/scala-js,SebsLittleHelpers/scala-js,mdedetrich/scala-js,xuwei-k/scala-js,spaced/scala-js,spaced/scala-js,jasonchaffee/scala-js,sjrd/scala-js,japgolly/scala-js,mdedetrich/scala-js,jasonchaffee/scala-js,japgolly/scala-js,nicolasstucki/scala-js,xuwei-k/scala-js,scala-js/scala-js,nicolasstucki/scala-js,lrytz/scala-js,xuwei-k/scala-js,gzm0/scala-js,mdedetrich/scala-js,ummels/scala-js,ummels/scala-js