[SILGen] Separate the initialization of a wrapped property from a wrapped value

Teach SILGen to emit a separate SIL function to capture the
initialization of the backing storage type for a wrapped property
based on the wrapped value. This eliminates manual code expansion at
every use site.

lib/SILGen/SILGenProlog.cpp

@@ -547,4 +547,3 @@ uint16_t SILGenFunction::emitProlog(ParameterList *paramList,
 
   return ArgNo;
 }
-