fix #18627(Program segfaults with ARC when using openArray[string]) (#18713)

* fix #18627
* add testcase
* rename
* another
* remove tyVarargs

tests/arc/topenarray.nim

@@ -0,0 +1,24 @@
+discard """
+  input: "hi"
+  output: '''
+hi
+Nim
+'''
+  matrix: "--gc:arc -d:useMalloc; --gc:arc"
+"""
+block: # bug 18627
+  proc setPosition(params: openArray[string]) =
+    for i in params.toOpenArray(0, params.len - 1):
+      echo i
+
+  proc uciLoop() =
+    let params = @[readLine(stdin)]
+    setPosition(params)
+
+  uciLoop()
+
+  proc uciLoop2() =
+    let params = @["Nim"]
+    for i in params.toOpenArray(0, params.len - 1):
+      echo i
+  uciLoop2()