out parameters: enforce that 'out' is only used as a parameter (#20510)

* out parameters: enforce that 'out' is only used as a parameter

* make tables.nim use 'out' parameters

* better backwards compat

compiler/typeallowed.nim

@@ -65,6 +65,8 @@ proc typeAllowedAux(marker: var IntSet, typ: PType, kind: TSymKind,
     elif t.kind == tyLent and ((kind != skResult and views notin c.features) or
                               kind == skParam): # lent can't be used as parameters.
       result = t
+    elif isOutParam(t) and kind != skParam:
+      result = t
     else:
       var t2 = skipTypes(t[0], abstractInst-{tyTypeDesc, tySink})
       case t2.kind