This makes two major improvements:
(1) WiredTiger "metadata:create" cursors are very expensive; only use
these when absolutely necessary, and use standard "metadata:" cursors
everywhere else. This lowers startup calls to "metadata:create" from 3
to 1 per table.
(2) No longer open a cursor for every WiredTiger collection at startup.
Instead, lazily open cursors to initialize RecordIDs for inserts.
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