Fix static/proto initializers when there aren't class fields

[JLHwung]

Q	A
Fixed Issues?	Fixes #14334 (comment)
Patch: Bug Fix?	Yes
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

The helper behaviour is now strictly aligned with the transformer:

babel/packages/babel-plugin-proposal-decorators/src/transformer-2021-12.ts

Lines 734 to 740 in 0b29359

	if (kind !== FIELD) {
	if (isStatic) {
	requiresStaticInit = true;
	} else {
	requiresProtoInit = true;
	}
	}

Also added a script per #14334 (comment). Here is an an example output when we have uncommitted changes after build

Please re-run "make build" and checkout the following changes to git
HEAD detached at pull/14335/merge
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   packages/babel-helpers/src/helpers-generated.ts

no changes added to commit (use "git add" and/or "git commit -a")

/cc @wvq Please try if this PR fixes the issues you found when using decorators. Thank you!

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/51422/

[nicolo-ribaudo]

Nit, but this probably produces a smaller output: initializers = staticInitializers = staticInitializers || [].

[nicolo-ribaudo]

Ah no it's ok, the minifier step already produces this code.

[JLHwung]

initializers = staticInitializers = staticInitializers || []

This is the exact output in helpers-generated by terser, so I don't bother to manually minify here.

[nicolo-ribaudo]

Code looks good, let's see if the new CI check already catches some missing files 😬

[wvq]

:) It's work's now.

[nicolo-ribaudo]

I slightly updated the PR title so that it fits in a commit message even with (#14335) at the end :)