ARROW-11709: [Rust][DataFusion] Move expressions and inputs into LogicalPlan ratherthan helpers in util

[alamb]

Rationale

Goal is to consolidate the expression walking in one place as part of my longer term plan to make plan rewriting avoid so much copying in the DataFusion optimizer (https://issues.apache.org/jira/browse/ARROW-11689). This is setting the stage for LogicalPlans to be able to rewrite themselves rather than being rewritten by the optimizer utils

Changes

move expressions and inputs into LogicalPlan rather than helpers in util. There are no logic changes.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-11709

[codecov-io]

Codecov Report

Merging #9568 (aefb5c2) into master (5bea624) will increase coverage by 0.12%.
The diff coverage is 89.31%.

@@            Coverage Diff             @@
##           master    #9568      +/-   ##
==========================================
+ Coverage   82.25%   82.38%   +0.12%     
==========================================
  Files         244      244              
  Lines       55685    56221     +536     
==========================================
+ Hits        45806    46319     +513     
- Misses       9879     9902      +23     

Impacted Files	Coverage Δ
rust/datafusion/src/logical_plan/expr.rs	81.56% <ø> (+0.42%)	⬆️
...ion-testing/src/bin/arrow-json-integration-test.rs	0.00% <0.00%> (ø)
rust/arrow/src/ipc/writer.rs	87.23% <50.00%> (-0.59%)	⬇️
rust/datafusion/src/logical_plan/plan.rs	79.59% <58.53%> (-2.86%)	⬇️
...datafusion/src/physical_plan/string_expressions.rs	77.00% <82.23%> (+7.37%)	⬆️
rust/parquet/src/arrow/array_reader.rs	77.61% <91.30%> (-0.02%)	⬇️
rust/datafusion/src/physical_plan/functions.rs	85.52% <91.42%> (+11.69%)	⬆️
rust/datafusion/src/optimizer/constant_folding.rs	94.46% <100.00%> (ø)
rust/datafusion/src/optimizer/filter_push_down.rs	97.65% <100.00%> (ø)
...datafusion/src/optimizer/hash_build_probe_order.rs	55.31% <100.00%> (ø)
... and 20 more

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[alamb]

FYI @Dandandan and @houqp

[Dandandan]

Makes sense, LGTM