MB-30253 - regexp.dfaBuilder preallocs insts array
MB-30253 - regexp.dfaBuilder preallocs insts array

This change avoids slice growing during append()'s.

From a bleve-query microbenchmark on 50K doc wikipedia dataset, using
a regexp query-string for a low-frequency term, like
"text:stephensons*", throughput went from 1133 q/sec to 1400 q/sec
after the change.

Change-Id: I4de5a33ea56f7e63cded2d956781f59faa08b94a
Reviewed-on: http://review.couchbase.org/96082
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>
Tested-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>

couchbase/vellum