ARROW-5830: [C++] Stop using memcmp in TensorEquals for tensors with float values

[mrkn]

memcmp is an inappropriate way to examine the equality of float tensors because float tensors can have NaNs. In addition to fix this issue, I made the following fixes in this pull request:

• Change the namespace of StridedIntegerTensorContentsEquals, that is renamed from StridedTensorContentsEquals, to anonymous because it isn't referred from the outside of compare.cc
• Let the result of Tensor::Equals be false when two tensors has the different shapes.

[mrkn]

I think this pull-request is ready for code review.

@wesm Could you please have a look?

[codecov-io]

Codecov Report

Merging #5166 into master will increase coverage by 1.61%.
The diff coverage is 99.24%.

@@            Coverage Diff             @@
##           master    #5166      +/-   ##
==========================================
+ Coverage   87.65%   89.27%   +1.61%     
==========================================
  Files        1025      742     -283     
  Lines      146568   106041   -40527     
  Branches     1437        0    -1437     
==========================================
- Hits       128480    94668   -33812     
+ Misses      17726    11373    -6353     
+ Partials      362        0     -362

Impacted Files	Coverage Δ
cpp/src/arrow/compare.h	100% <ø> (ø)	⬆️
cpp/src/arrow/tensor.cc	96.51% <100%> (+0.04%)	⬆️
cpp/src/arrow/tensor.h	91.42% <100%> (+0.25%)	⬆️
cpp/src/arrow/tensor_test.cc	100% <100%> (ø)	⬆️
cpp/src/arrow/compare.cc	81.24% <98.36%> (+1.33%)	⬆️
r/R/arrow-package.R	63.63% <0%> (-36.37%)	⬇️
cpp/src/arrow/util/iterator.h	84.84% <0%> (-15.16%)	⬇️
cpp/src/parquet/thrift.h	86.13% <0%> (-7.9%)	⬇️
cpp/src/arrow/dataset/file_base.h	87.5% <0%> (-5.36%)	⬇️
cpp/src/arrow/util/compression.cc	82.14% <0%> (-4.96%)	⬇️
... and 336 more

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[wesm]

I'm traveling this week but I will try to review.

Note that I just opened https://issues.apache.org/jira/browse/ARROW-6359, your comments would be welcome

[mrkn]

@wesm I noticed that TensorEquals should also have an optional parameter of EqualOptions.
I want to make a change to add it by this Wednesday, please wait a moment.

And I'll look at ARROW-6359. Thank you for telling me.

[mrkn]

I've finished working for EqualOptions support in Tensor::Equals.
This is finally ready to review.

[pitrou]

The size-based clause needs fixing as mentioned in the comments. Otherwise, LGTM.

[pitrou]

Thank you @mrkn !

[codecov-commenter]

Codecov Report

❌ Patch coverage is 99.24812% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.27%. Comparing base (0f9c4a9) to head (a74ad03).

Files with missing lines	Patch %	Lines
cpp/src/arrow/compare.cc	98.36%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5166      +/-   ##
==========================================
+ Coverage   87.65%   89.27%   +1.61%     
==========================================
  Files        1025      742     -283     
  Lines      146568   106041   -40527     
  Branches     1437        0    -1437     
==========================================
- Hits       128480    94668   -33812     
+ Misses      17726    11373    -6353     
+ Partials      362        0     -362     

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