iterator: TableFilter option about pebble HOT 1 CLOSED

Provide an API for cloning an iterator (with new options) that returns a new iterator pinned to the same visible sequence number.

I'm currently not seeing a need for this now that an iterator can switch between prefix and normal iteration mode.

The only remaining item here is IterOptions.TableFilter:

// TableFilter can be used to filter the tables that are scanned during
// iteration based on the user properties. Return true to scan the table and
// false to skip scanning.
//
// TableFilter func(userProps map[string]string) bool

This shouldn't be particularly difficult, though we'll also have to add support for a table properties collector interface in order to populate user maintained table properties.

from pebble.