Fix the .pos.point of Bind nodes

The point of a definition should be the position of the first letter in
the name of a definition. For a `Bind` node this is just the
start (previously we were using the position of the `:`).

Author: smarter

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1155,7 +1155,8 @@ object Parsers {
         t
     }
 
-    def ascription(t: Tree, location: Location.Value) = atPos(startOffset(t), in.skipToken()) {
+    def ascription(t: Tree, location: Location.Value) = atPos(startOffset(t)) {
+      in.skipToken()
       in.token match {
         case USCORE =>
           val uscoreStart = in.skipToken()