store full definition AST for consts, fix noRewrite (#20115)

* continue #9582 for consts, close #9331, fix #20114

also move extractPragma to ast to pave the way for things like {.strdefine: "abc".} etc

* changelog correctly

* fix jsgen

* update tgetimpl

* fix sighashes

* fix #19766, add comment about postfix

* fix noRewrite LOL

refs #16620

* fix changelog

* fix destructors

tests/trmacros/tnorewrite.nim

@@ -0,0 +1,20 @@
+block:
+  proc get(x: int): int = x
+
+  template t{get(a)}(a: int): int =
+    {.noRewrite.}:
+      get(a) + 1
+
+  doAssert get(0) == 1
+
+block:
+  var x: int
+
+  template asgn{a = b}(a: int{lvalue}, b: int) =
+    let newVal = b + 1
+    # ^ this is needed but should it be?
+    {.noRewrite.}:
+      a = newVal
+
+  x = 10
+  doAssert x == 11, $x

tests/trmacros/trmacros_various.nim

@@ -33,7 +33,8 @@ block tcse:
 
 block hoist:
   template optPeg{peg(pattern)}(pattern: string{lit}): Peg =
-    var gl {.global, gensym.} = peg(pattern)
+    {.noRewrite.}:
+      var gl {.global, gensym.} = peg(pattern)
     gl
   doAssert match("(a b c)", peg"'(' @ ')'")
   doAssert match("W_HI_Le", peg"\y 'while'")