ARROW-17458: [C++] Cast between decimal and string

[quanghgx]

• Update cast_string and cast_decimal function kernels to support string <--> decimal
• Rely on existing converter/parser: Decimal::ToString, Decimal::FromString
• Follow current layout closely

Relates to: https://issues.apache.org/jira/browse/ARROW-17042 and https://issues.apache.org/jira/browse/ARROW-17458

[github-actions]

https://issues.apache.org/jira/browse/ARROW-17458

[github-actions]

⚠️ Ticket has not been started in JIRA, please click 'Start Progress'.

[quanghgx]

Hi @westonpace
This PR is ready for review. It relates to both ARROW-17042 and ARROW-17458

For 2 failed CI checks, it seems, they are not related to this change set:
https://github.com/apache/arrow/actions/runs/3302286318/jobs/5448920608#step:6:2863
https://github.com/apache/arrow/actions/runs/3302286320/jobs/5448920508#step:7:7533

Sincerely,

[westonpace]

I'm not an expert in the compute kernel but this looks pretty complete to me. I just have one small question. Thanks for the contribution.

[ursabot]

Benchmark runs are scheduled for baseline = b87370d and contender = e9f0b3f. e9f0b3f is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Finished ⬇️0.0% ⬆️0.0%] ec2-t3-xlarge-us-east-2
[Failed ⬇️0.0% ⬆️0.0%] test-mac-arm
[Finished ⬇️0.27% ⬆️0.0%] ursa-i9-9960x
[Failed ⬇️0.04% ⬆️0.0%] ursa-thinkcentre-m75q
Buildkite builds:
[Finished] e9f0b3f7 ec2-t3-xlarge-us-east-2
[Failed] e9f0b3f7 test-mac-arm
[Finished] e9f0b3f7 ursa-i9-9960x
[Failed] e9f0b3f7 ursa-thinkcentre-m75q
[Finished] b87370d6 ec2-t3-xlarge-us-east-2
[Failed] b87370d6 test-mac-arm
[Finished] b87370d6 ursa-i9-9960x
[Finished] b87370d6 ursa-thinkcentre-m75q
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