Add numeric typed equivalents to StrField

There ought to be numeric typed equivalents to StrField in the schema. The TrieField types can be configured to do this with precisionStep=0, but the TrieFields are deprecated and slated for removal in 8.0. PointFields may be adequate for some use cases but, unlike TrieField, it's not as efficient for simple field:value lookup queries. They probably should use the same internal sortable full-precision term format that TrieField uses (details currently in LegacyNumericUtils (which are used by the deprecated Trie fields).