Use code points instead of grapheme clusters for string functions

[Dandandan]

Which issue does this PR close?

Closes #3049

Rationale for this change

Matching PostgreSQL, Spark and improve performance. Overall simplification.

What changes are included in this PR?

Moves most functions, except rpad, lpad and translate to use code points rather than grapheme clusters.
Also code simplification & avoiding some allocations.

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #3054 (12d7366) into master (a8ed874) will increase coverage by 0.03%.
The diff coverage is 79.31%.

@@            Coverage Diff             @@
##           master    #3054      +/-   ##
==========================================
+ Coverage   85.84%   85.88%   +0.03%     
==========================================
  Files         289      289              
  Lines       51862    51844      -18     
==========================================
+ Hits        44520    44525       +5     
+ Misses       7342     7319      -23     

Impacted Files	Coverage Δ
...atafusion/physical-expr/src/unicode_expressions.rs	77.45% <76.92%> (+4.35%)	⬆️
datafusion/core/tests/sql/unicode.rs	100.00% <100.00%> (ø)
datafusion/physical-expr/src/functions.rs	92.72% <100.00%> (ø)
datafusion/expr/src/logical_plan/plan.rs	77.43% <0.00%> (-0.18%)	⬇️
datafusion/core/tests/sql/timestamp.rs	100.00% <0.00%> (ø)
datafusion/expr/src/window_frame.rs	93.27% <0.00%> (+0.84%)	⬆️

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[alamb]

cc @ovr

[Dandandan]

@alamb @andygrove this is reviewable now.

[andygrove]

LGTM. I assume there should be a documentation update as well as part of this PR? Perhaps the rustdoc for fn character_length should explain how this is now implemented?

[alamb]

Looks like a nice simplification and improvement to me ❤️ Thank you @Dandandan

cc @ovr who I think contributed the original implementation

[ovr]

cc @ovr who I think contributed the original implementation

LGTM, but I am not an original author 😄

[Dandandan]

I think this was @seddonm1

[andygrove]

LGTM. Thanks @Dandandan

[ursabot]

Benchmark runs are scheduled for baseline = a4fa44f and contender = 88f6548. 88f6548 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java