macros: Introduce sameType(a, b) for node types

Previously introduced node comparison `==` was working somehow wrong on nodes
returned from getType(a), comparing just ids of the symbols.

Recently introduced `==` change 47dce26886
started comparing symbol nodes pointer-wise, thus strictly. Since getType(a)
always creates new symbol pointing to the type, comparing two such nodes using
`==` always returns false, even they point to the same type.

That is why we need a new sameType macro to be able to tell if these nodes
point to the same type.

tests/macros/tsametype.nim

@@ -0,0 +1,41 @@
+discard """
+output: '''1
+0
+1
+0
+1
+0
+1
+0
+1
+0'''
+"""
+
+import macros
+
+macro same(a: typedesc, b: typedesc): expr =
+  newLit(a.getType[1].sameType b.getType[1])
+
+echo same(int, int)
+echo same(int, float)
+
+type
+  SomeInt = int
+  DistinctInt = distinct int
+  SomeFloat = float
+  DistinctFloat = distinct float
+
+echo same(int, SomeInt)
+echo same(int, DistinctInt)
+echo same(float, SomeFloat)
+echo same(float, DistinctFloat)
+
+type
+  Obj = object of RootObj
+  SubObj = object of Obj
+  Other = object of RootObj
+
+echo same(Obj, Obj)
+echo same(int, Obj)
+echo same(SubObj, SubObj)
+echo same(Other, Obj)