TMUDF C++ compiler interface, part of log-reading TMUDF

This is the infrastructure for a new C++ interface for TMUDFs
(table-mapping UDFs). It is used by a new log-reading TMUDF that
is not yet complete, but should be finished in the next few days.

See blueprint cmp-tmudf-compile-time-interface for more info.

Change-Id: I5a74e461462313b6d9722ac0deb21cd16c4b02ce
Merge "TMUDF C++ compiler interface, part of log-reading TMUDF"