tableam: Add table_finish_bulk_insert().

tableam: Add table_finish_bulk_insert().

This replaces the previous calls of heap_sync() in places using
bulk-insert. By passing in the flags used for bulk-insert the AM can
decide (first at insert time and then during the finish call) which of
the optimizations apply to it, and what operations are necessary to
finish a bulk insert operation.

Also change HEAP_INSERT_* flags to TABLE_INSERT, and rename hi_options
to ti_options.

These changes are made even in copy.c, which hasn't yet been converted
to tableam. There's no harm in doing so.

Author: Andres Freund
Discussion: https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de