fix(diagnostics): add 'set_semantic_meaning' to the side effects list

[pront]

Summary

This modifies internal state and it's return value is always returns null. Should not expect result usage.

This is true for all functions returning null so we could follow up with an enhancement to the unused expression detector.

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

How did you test this PR?

Pointed Vector to this VRL branch and tested with:

sources:
  demo_logs:
    type: demo_logs
    format: json
transforms:
  remap:
    type: remap
    inputs: [demo_logs]
    source: |
      set_semantic_meaning(.foo, "a")
      .foo = "bar"
sinks:
  console:
    type: console
    inputs: [remap]
    encoding:
      codec: json

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on
  our guidelines.
• No. A maintainer will apply the "no-changelog" label to this PR.

Checklist

• Our CONTRIBUTING.md is a good starting place.
• If this PR introduces changes to LICENSE-3rdparty.csv, please
  run dd-rust-license-tool write and commit the changes. More details here.
• For new VRL functions, please also create a sibling PR in Vector to document the new function.

References

• Closes: VRL compiler warns about the unused result of set_semantic_meaning #1149