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ARROW-12123: [Rust][DataFusion] Use smallvec for indices for better join performance

This is better for the common case where (almost) every value in the build side will be unique, and thus will be store once per this list, avoiding heap allocations and extra indirections (not saving the index inline but in a different  `Vec`).

this is a ~7.5% improvement for TCP-H query 5 (SF=1, 16 partitions/threads, loaded in memory).

master:
`Query 5 avg time: 155.83 ms`

PR:
`Query 5 avg time: 144.18 ms`

Closes #9826 from Dandandan/smallvec_join

Authored-by: Heres, Daniel <danielheres@gmail.com>
Signed-off-by: Andrew Lamb <andrew@nerdnetworks.org>