[FEA] Add various new table operations

[sleeepyjack]

Part of #110 (Refactor of open address data structures)

Development branch: NVIDIA/cuCollections/refactor

TODOs

• Check if element is present in the data structure: is_present (alias for contains) + is_absent
• Re-initialize the data structure: clear (already supported by some data structures under the alias initialize.
• Rebuild data structure with different size: rehash (see [FEA] static_map::rehash  #21)
• Higher-order function for_each(key, func, ...) which applies func to all slots that are equivalent to key. (see https://github.com/sleeepyjack/warpcore/blob/master/include/warpcore/single_value_hash_table.cuh#L506 and https://github.com/sleeepyjack/warpcore/blob/master/include/warpcore/multi_value_hash_table.cuh#L607)

[PointKernel]

One reduce instead of two ballots to potentially improve contains: https://godbolt.org/z/qv6Ghv8M3

Not necessarily improve the performance, worth testing though

[PointKernel]

is_absent and is_present turns out to be just contains + output iterator if needed.

Completed