fixed dot operator recursive loop & macro suggest (#16922)

* basic stability improvements; refs nimsuggest
* fixed dot operator recursive loop & macro suggest
* hacky fix for run away dot operator sem check

Committing this mostly to make the issue more clear. Perhaps get better
feedback.

* semExprWithType seems like a better place to check
* fixed error messages const case expressions
* Clean-up test
* stopped the dot operator madness

No longer get infinite recursion when seming broken code with a dot
operator macro like in jsffi.

Co-authored-by: Araq <rumpf_a@web.de>

compiler/semtypinst.nim

@@ -229,6 +229,8 @@ proc replaceTypeVarsN(cl: var TReplTypeVars, n: PNode; start=0): PNode =
     n = reResolveCallsWithTypedescParams(cl, n)
     result = if cl.allowMetaTypes: n
              else: cl.c.semExpr(cl.c, n)
+    if not cl.allowMetaTypes:
+      assert result.kind notin nkCallKinds
   else:
     if n.len > 0:
       newSons(result, n.len)