tests and docs for call operator (#16980)

* tests and docs for call operator

* fix leftover

* add extra dot test

tests/specialops/tcallprecedence.nim

@@ -0,0 +1,44 @@
+import macros
+
+{.experimental: "dotOperators".}
+{.experimental: "callOperator".}
+
+block:
+  template `.()`(foo: int, args: varargs[untyped]): untyped {.used.} =
+    ".()"
+
+  template `()`(foo: int, args: varargs[untyped]): untyped =
+    "()"
+
+  let a = (b: 1)
+  let c = 3
+
+  doAssert a.b(c) == "()"
+  doAssert not compiles(a(c))
+  doAssert (a.b)(c) == "()"
+
+macro `()`(args: varargs[typed]): untyped =
+  result = newLit("() " & args.treeRepr)
+
+macro `.`(args: varargs[typed]): untyped =
+  result = newLit(". " & args.treeRepr)
+
+block:
+  let a = 1
+  let b = 2
+  doAssert a.b == `()`(b, a)
+
+block:
+  let a = 1
+  proc b(): int {.used.} = 2
+  doAssert a.b == `.`(a, b)
+
+block:
+  let a = 1
+  proc b(x: int): int = x + 1
+  let c = 3
+
+  doAssert a.b(c) == `.`(a, b, c)
+  doAssert a(b) == `()`(a, b)
+  doAssert (a.b)(c) == `()`(a.b, c)
+  doAssert a.b == b(a)