SI-7331 tb.parse returns unpositioned trees

This commit gets rid off code wrapping that was previously used by
toolbox to get into correct parsing mode. Instead combination of
templateStats/accept(EOF) is used. This is the same solution as the one
used in repl and built-in scriptRunner

This pull request doesn't attempt to generalize this approach in any
way and re-use it all over the place due to the caution of possible
accidental compatibility breakage. I plan to do it separately against
master.

Additionally there are a few more changes that make importers be aware
of positions and a test for that (via @jedesah).
Merge pull request #2800 from densh/topic/toolbox-positions

SI-7331 tb.parse returns unpositioned trees