genTryCpp to catch by Nim type, ready for first review (#7196)

* Rewrite genTryCpp

* correction

* Implement polymorphic raise in cpp

* revert backticks in emit

* Cleanp a comment

* revert test changes

* better handling of <new> header

lib/system/excpt.nim

@@ -320,7 +320,7 @@ proc raiseExceptionAux(e: ref Exception) =
       quitOrDebug()
     else:
       pushCurrentException(e)
-      {.emit: "throw NimException(`e`, `e`->name);".}
+      {.emit: "`e`->raise();".}
   else:
     if excHandler != nil:
       if not excHandler.hasRaiseAction or excHandler.raiseAction(e):