Add support for a CHANNEL language toggle

It is common on dual language systems to have an IVR menu entry to toggle the language to the other supported language. At present, to do this in the GUI you must have two different IVR's and two different Language options to make this work. I have used the following with a Custom Destination to toggle channel language without duplicating IVRs, but it would be a useful addition for the GUI to have a single FreePBX destination capable of toggling between two channel languages:

[english-french-toggle]
exten => s,1,Noop(Entering user defined context english-french-toggle in extensions_custom.conf)
exten => s,n,goto(english-french-toggle,${CHANNEL(language)},1)  ;  goto whatever language channel is currently set to
exten => s,n,return
 
; if channel is currently english, set to french
exten => en,1,Set(CHANNEL(language)=fr)
exten => en,n,return
 
; if channel is currently french, set to english
exten => fr,1,Set(CHANNEL(language)=en)
exten => fr,n,return
 
; catchall for failsafe, return back to FreePBX call flow if channel is neither
exten => _.,1,return