custom integer literals (#17489)

* user defined integer literals; refs #17020
* updated renderer.nim
* use mlexerutils helper
* imported all test cases from https://github.com/nim-lang/Nim/pull/17020
* final grammar updated

tests/lexer/tunary_minus.nim

@@ -6,13 +6,7 @@ discard """
 
 import std/[macros, strutils]
 
-macro lispReprStr*(a: untyped): untyped = newLit(a.lispRepr)
-
-macro assertAST*(expected: string, struct: untyped): untyped =
-  var ast = newLit(struct.treeRepr)
-  result = quote do:
-    if `ast` != `expected`:
-      doAssert false, "\nGot:\n" & `ast`.indent(2) & "\nExpected:\n" & `expected`.indent(2)
+import mlexerutils
 
 const one = 1
 const minusOne = `-`(one)