chore(stdlib): create macro to keep exports and stdlib in sync

[thomasqueirozb]

Summary

This macro prevents functions from being exported but not included in the stdlib. Should make maintenence better and prevent issues like #1553 from happening

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?

I verified # of imports before (200) and lines inside the macro (199). It is 199 since pub use get_timezone_name::get_name_for_timezone isn't and shouldn't be included inside all().

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

[pront]

This is a pretty good improvement over what we have today.

[pront]

Note for posterity: This PR is an improvement (since now the contributor needs to add the new function name in one place only) but not a real fix. One fix would be to add a test that detects missing function names based on stdlib contents. There might be better alternatives, e.g. generate this list in a build.rs.