PRE: Set value count in splitAndTransfer
PRE: Handling directories in FormatMatcher
PRE: Add "append" concept to directory write.

* This is so stats can be stored in [table].stats.drill and be appended to be writing a new file into the directory.
FUNCS: Statistics functions as UDFs:
Currently using FieldReader to ensure consistent output type so that Unpivot doesn't get confused. All stats columns should be Nullable, so that stats functions can return NULL when N/A.
* custom versions of "count" that always return BigInt
* HyperLogLog based NDV that returns BigInt that works only on VarChars
* HyperLogLog with binary output that only works on VarChars
OPS: Updated protobufs for new ops
OPS: Implemented StatisticsAggregate
OPS: Implemented StatisticsUnpivot
ANALYZE: AnalyzeTable functionality
* JavaCC syntax more-or-less copied from LucidDB.
* (Basic) AnalyzePrule: DrillAnalyzeRel -> UnpivotPrel and StatsAggPrel
ANALYZE: Add getMetadataTable() to AbstractSchema
USAGE: Change field access in QueryWrapper
USAGE: Add getDrillTable() to DrillScanRelBase and ScanPrel
* since ScanPrel does not inherit from DrillScanRelBase, this requires adding a DrillTable to the constructor
* This is done so that a custom ReflectiveRelMetadataProvider can access the DrillTable associated with Logical/Physical scans.
USAGE: Attach DrillTableMetadata to DrillTable.
* DrillTableMetadata represents the data scanned from a corresponding ".stats.drill" table
* In order to avoid doing query execution right after the ".stats.drill" table is found, metadata is not actually collected until the MaterializationVisitor is used.
** Currently, the metadata source must be a string (so that a SQL query can be created). Doing this with a table is probably more complicated.
** Query is set up to extract only the most recent statistics results for each column.
USAGE: Configure DrillJoinRelBase to use NDV metadata when available.
USAGE: attach metadata to table
USAGE: implement optic providers
TEST