Fix #5691 (#15158)

* Fix #5691
* Cleanup and thoughts
* Use scope approach
* Seperate defined/declared/declaredInScope magics
* Fix declaredInScope
* Update spec accordingly

doc/manual.rst

@@ -5019,23 +5019,16 @@ delayed until template instantiation time:
     :status: 1
 
   template t(body: typed) =
+    proc p = echo "hey"
     block:
       body
 
   t:
-    var i = 1
-    echo i
+    p()  # fails with 'undeclared identifier: p'
 
-  t:
-    var i = 2  # fails with 'attempt to redeclare i'
-    echo i
-
-The above code fails with the mysterious error message that ``i`` has already
-been declared. The reason for this is that the ``var i = ...`` bodies need to
-be type-checked before they are passed to the ``body`` parameter and type
-checking in Nim implies symbol lookups. For the symbol lookups to succeed
-``i`` needs to be added to the current (i.e. outer) scope. After type checking
-these additions to the symbol table are not rolled back (for better or worse).
+The above code fails with the error message that ``p`` is not declared.
+The reason for this is that the ``p()`` body is type-checked before getting
+passed to the ``body`` parameter and type checking in Nim implies symbol lookups.
 The same code works with ``untyped`` as the passed body is not required to be
 type-checked:
 
@@ -5043,16 +5036,12 @@ type-checked:
     :test: "nim c $1"
 
   template t(body: untyped) =
+    proc p = echo "hey"
     block:
       body
 
   t:
-    var i = 1
-    echo i
-
-  t:
-    var i = 2  # compiles
-    echo i
+    p()  # compiles
 
 
 Varargs of untyped