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/pragmas/tcustom_pragma.nim

@@ -439,3 +439,43 @@ when false:
 
   # left-to-right priority/override order for getCustomPragmaVal
   assert bb.getCustomPragmaVal(hehe) == (key: "hi", val: "hu", haha: "he")
+
+{.experimental: "dynamicBindSym".}
+
+# const
+block:
+  template myAttr() {.pragma.}
+  template myAttr2(x: int) {.pragma.}
+  template myAttr3(x: string) {.pragma.}
+
+  type
+    MyObj2 = ref object
+
+  const a {.myAttr,myAttr2(2),myAttr3:"test".}: int = 0
+  const b {.myAttr,myAttr2(2),myAttr3:"test".} = 0
+
+  macro forceHasCustomPragma(x: untyped, y: typed): untyped =
+    var x = bindSym(x.repr)
+    for c in x:
+      if c.symKind == nskConst:
+        x = c
+        break
+    result = getAst(hasCustomPragma(x, y))
+
+  macro forceGetCustomPragmaVal(x: untyped, y: typed): untyped =
+    var x = bindSym(x.repr)
+    for c in x:
+      if c.symKind == nskConst:
+        x = c
+        break
+    result = getAst(getCustomPragmaVal(x, y))
+
+  template check(s: untyped) =
+    doAssert forceHasCustomPragma(s, myAttr)
+    doAssert forceHasCustomPragma(s, myAttr2)
+    doAssert forceGetCustomPragmaVal(s, myAttr2) == 2
+    doAssert forceHasCustomPragma(s, myAttr3)
+    doAssert forceGetCustomPragmaVal(s, myAttr3) == "test"
+
+  check(a)
+  check(b)