Add support for serializing ScalarValue::Dictionary to datafusion-proto

[alamb]

Which issue does this PR close?

Part of #3531

Rationale for this change

See #3531

What changes are included in this PR?

1. Implement serialization code for ScalarValue::Dictionary
2. Add tests
3. Explicitly list out unhandled variants so it is less likely we overlook new variants in the future. Turns out the following variants need to be completed (I will fix in follow on PRs):

Are there any user-facing changes?

One fewer bug

[codecov-commenter]

Codecov Report

Merging #3532 (c28d817) into master (9b22100) will increase coverage by 0.02%.
The diff coverage is 65.21%.

@@            Coverage Diff             @@
##           master    #3532      +/-   ##
==========================================
+ Coverage   85.77%   85.79%   +0.02%     
==========================================
  Files         299      300       +1     
  Lines       55360    55403      +43     
==========================================
+ Hits        47483    47532      +49     
+ Misses       7877     7871       -6     

Impacted Files	Coverage Δ
datafusion/proto/src/to_proto.rs	52.95% <42.85%> (-0.11%)	⬇️
datafusion/proto/src/from_proto.rs	40.02% <50.00%> (+0.09%)	⬆️
datafusion/proto/src/lib.rs	94.20% <100.00%> (+0.05%)	⬆️
datafusion/expr/src/window_frame.rs	92.43% <0.00%> (-0.85%)	⬇️
datafusion/expr/src/logical_plan/plan.rs	77.85% <0.00%> (ø)
...usion/core/src/physical_optimizer/parallel_sort.rs	100.00% <0.00%> (ø)
datafusion/core/src/execution/context.rs	79.31% <0.00%> (+0.02%)	⬆️
.../core/src/physical_plan/windows/window_agg_exec.rs	89.89% <0.00%> (+1.01%)	⬆️
...e/src/physical_plan/sorts/sort_preserving_merge.rs	93.81% <0.00%> (+1.23%)	⬆️
datafusion/core/src/physical_plan/sorts/sort.rs	94.37% <0.00%> (+1.27%)	⬆️

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[andygrove]

LGTM

[ursabot]

Benchmark runs are scheduled for baseline = 3a9e0d0 and contender = a6fbf24. a6fbf24 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