make two-argument withValues untyped (#26052)

The twp-argument form of `withValue` are expression when the branches
themselves are expressions.

tests/stdlib/ttables.nim

@@ -33,6 +33,22 @@ s2[p2] = 45_000
 s3[p1] = 30_000
 s3[p2] = 45_000
 
+block: # two-argument form of withValue forms expression
+  block: # Present
+    let sal = salaries.withValue(p1, sal):
+      sal[]
+    do:
+      0
+    doAssert sal == 30_000
+  block: # Missing
+    let sal = salaries.withValue(Person(), sal):
+      sal[]
+    do:
+      0
+    doAssert sal == 0
+  block: # Short form
+    doAssert salaries.withValue(p1, sal, sal[], 0) == 30_000
+
 block: # Ordered table should preserve order after deletion
   var
     s4 = initOrderedTable[int, int]()