Fixed #25848 -- Set template origin on each node.

Prior to 55f12f87, the template origin was available on each node via
`self.token.source[0]`. This behavior was removed when debug handling was
simplified, but 3rd-party debugging tools still depend on its presence.
This updates the Parser to set origin on individual nodes. This enables the
source template to be determined even when template extending or including is
used.