Error -> Defect for defects (#13908)

* Error -> Defect for defects

The distinction between Error and Defect is subjective,
context-dependent and somewhat arbitrary, so when looking at an
exception, it's hard to guess what it is - this happens often when
looking at a `raises` list _without_ opening the corresponding
definition and digging through layers of inheritance.

With the help of a little consistency in naming, it's at least possible
to start disentangling the two error types and the standard lib can set
a good example here.

tests/metatype/tunresolved_return_type.nim

@@ -11,7 +11,7 @@ type
 
 proc toNumber[T: int|uint|int64|uint64](v: ResultValue): T =
   if v < low(T) or v > high(T):
-    raise newException(RangeError, "protocol error")
+    raise newException(RangeDefect, "protocol error")
   return T(v)
 
 #proc toNumber[T](v: int32): T =