Fix code generation for json feature

[avantgardnerio]

Which issue does this PR close?

Closes #3366.

Rationale for this change

We want stable builds, and I broke that.

What changes are included in this PR?

Codegen into two separate files based upon selected features.

Are there any user-facing changes?

Builds work more reliably.

[avantgardnerio]

@alamb and @andygrove let's get this in before users start seeing random build issues. Sorry I didn't catch this with the initial PR.

[andygrove]

Thanks @avantgardnerio

[andygrove]

Is this something that we should have caught in CI?

[ursabot]

Benchmark runs are scheduled for baseline = ede82fb and contender = 827cab9. 827cab9 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

[avantgardnerio]

Is this something that we should have caught in CI?

Each CI job builds for a given feature set, then vaporizes the docker container. This is only something real users would encounter when switching feature sets back and forth, as I was doing trying to get a PR to pass all the tests.