Move find_typedef code from run_build.pl to src/tools/find_typedef in the Postgres repo

[tristan957]

I would like to make find_typdef available to extension authors, so they can properly use pgindent if they so choose.

After we have moved the code, it would be great if the buildfarm could just use the find_typedef script from Postgres.

Tom Lane suggested this idea, and I will try to be the champion of it. Copy-pasting code is easy to create the new src/tools/find_typedef, but making the buildfarm use this new script is the larger challenge. I was wondering if you had any suggestions :).