Can we "warm" SSDV ordinal maps on index reopen?

As rcmuir and jpountz pointed out in a discussion about facet benchmarks, we lazily build ordinal maps needed for SSDV faceting the first time we need them for a given index field instead of eagerly building them when the index is reopened. This puts an expensive penalty on the search path whenever an index is reloaded. Let's see if we can eagerly build these maps as part of reopening the index so the user doesn't get hit with this at search time.