ARROW-6085: [Rust] [DataFusion] Add traits for physical query plan

[andygrove]

This is the first of quite a few PRs to add support for parallel (multi-threaded) query execution based on the PoC in #4221

[sunchao]

LGTM

[codecov-io]

Codecov Report

Merging #4975 into master will decrease coverage by 4.81%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #4975       +/-   ##
===========================================
- Coverage   87.54%   82.73%    -4.82%     
===========================================
  Files        1000       87      -913     
  Lines      142351    25430   -116921     
  Branches     1418        0     -1418     
===========================================
- Hits       124625    21040   -103585     
+ Misses      17364     4390    -12974     
+ Partials      362        0      -362

Impacted Files	Coverage Δ
python/pyarrow/ipc.pxi
cpp/src/arrow/csv/chunker-test.cc
cpp/src/parquet/column_page.h
cpp/src/parquet/bloom_filter-test.cc
cpp/src/arrow/array/builder_decimal.cc
r/src/symbols.cpp
cpp/src/arrow/io/test-common.h
cpp/src/arrow/util/int-util-test.cc
cpp/src/arrow/python/io.cc
python/pyarrow/hdfs.py
... and 903 more

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