ast: Update rule index to support glob.match

These changes update the rule index to support glob.match calls. The
changes update the build step to transform glob.match(pattern,
delimiter, match) calls into ref/value pairs like equality
expressions. In addition, the build step creates a mapper function
that transforms resolved values into lookup values during traversal.

As part of these changes, the build operation has been refactored so
that most of the process is encapsulated by a new refindices struct
that's separate from the actual rule index/trie. Hopefully this makes
the code easier to follow.

The index build step for glob.match only recognizes statements where
the match operand was given as a reference (and then was rewritten by
the earlier step in the compiler.) If this is too brittle we could
revisit the build step and close over all intermediate assignments.

Fixes #1496

Signed-off-by: Torin Sandall <torinsandall@gmail.com>