ARROW-11369: [DataFusion] Split physical_plan/expressions.rs

[jorgecarleitao]

This PR splits the +4k LOC expressions.rs module in modules, one per expression, thereby making it easier to navigate and work with.

No backward incompatible changes are expected from this.

Each commit is an independent expression / logical change.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-11369

[codecov-io]

Codecov Report

Merging #9312 (446d5ad) into master (437c8c9) will increase coverage by 0.00%.
The diff coverage is 81.25%.

@@ Coverage Diff @@## master #9312 +/- ##
=======================================
Coverage 81.88% 81.89% =======================================
Files 215 230 +15 Lines 52988 53004 +16 =======================================
+ Hits 43391 43407 +16 
Misses 9597 9597 

Impacted Files	Coverage Δ
...tafusion/src/physical_plan/expressions/negative.rs	42.85% <42.85%> (ø)
...datafusion/src/physical_plan/expressions/column.rs	70.00% <70.00%> (ø)
...st/datafusion/src/physical_plan/expressions/not.rs	70.83% <70.83%> (ø)
...usion/src/physical_plan/expressions/is_not_null.rs	72.41% <72.41%> (ø)
...atafusion/src/physical_plan/expressions/is_null.rs	72.41% <72.41%> (ø)
...t/datafusion/src/physical_plan/expressions/case.rs	73.29% <73.29%> (ø)
...atafusion/src/physical_plan/expressions/in_list.rs	75.37% <75.37%> (ø)
...st/datafusion/src/physical_plan/expressions/sum.rs	78.28% <78.28%> (ø)
...tafusion/src/physical_plan/expressions/coercion.rs	78.65% <78.65%> (ø)
...atafusion/src/physical_plan/expressions/average.rs	83.78% <83.78%> (ø)
... and 22 more

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[jorgecarleitao]

The clippy error is unrelated.

[alamb]

Thanks @jorgecarleitao -- this is great. ❤️

I went through the PR commit by commit spot checked things -- everything looked good to me though clearly I did not go through all the changes in detail.

FYI @seddonm1 in case this conflicts with work you are working on

[alamb]

Clippy error is addressed here: #9314

[seddonm1]

Thanks @alamb and @jorgecarleitao . Good idea. I'll rebase and apply these changes. I think the next work will be to address the signatures so I'll be starting work again tomorrow.

[andygrove]

Thanks a lot for doing this @jorgecarleitao

[alamb]

🎉