Add proc [](n: NimNode, s: HSlice[T, U]): seq[NimNode] to macros (#7735)

fixes #7670.

tests/macros/tslice.nim

@@ -0,0 +1,38 @@
+import macros
+
+macro test(): untyped =
+  result = nnkStmtList.newTree()
+  let n = nnkStmtList.newTree(
+    newIdentNode("one"),
+    newIdentNode("two"),
+    newIdentNode("three"),
+    newIdentNode("four"),
+    newIdentNode("five"),
+    newIdentNode("six")
+  )
+
+  var i = 1
+  for x in n[1 .. ^2]:
+    assert x == n[i]
+    i.inc
+  assert i == 5
+
+  i = 3
+  for x in n[3..^1]:
+    assert x == n[i]
+    i.inc
+  assert i == 6
+
+  i = 0
+  for x in n[0..3]:
+    assert x == n[i]
+    i.inc
+  assert i == 4
+
+  i = 0
+  for x in n[0..5]:
+    assert x == n[i]
+    i.inc
+  assert i == 6
+
+test()