Now that we have codified the use of FIXME comments in WT source code (see WT-15810), we should add a script to check for references to tickets that don't match that format in the source code and run it as part of our pre-merge testing (presumably as part of the s_all suite).

Specifically we should report as an error any source file in the WT library that

• Cites a WT ticket without using the FIXME-WT-##### format
• Cites a ticket outside the WT project. 

For the latter it there are two approaches. I'm not sure which is best.

1. We could explicitly check for tickets from the obvious projects: SERVER, SLS, DOCS, STAR, WTBUILD, DEVPROD, HELP, BF, etc. This has the downside that if a new project is introduced, we wouldn't automatically catch references to it.
2. We could check for a more general pattern. [A-Z][A-Z][1-9][0-9][0-9] currently only matches the FIXME-WT##### references in the WT tree, and those would be easy to filter out. It would match any ticket from a project with at least two letters and with 3 or more digits on the number. It has the downside that it could flag acronyms or other legitimate terms we might want to refer to. (I included three digits in the regular expression to avoid hits on CRC-32 and UTF-16, for example.)