fix(lib): esbuild helper functions injection not working with named exports

[sapphi-red]

Description

This is a regression caused by #14094

fixes #14537

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the PR Title Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[sapphi-red]

.* needs to be replaced with \s* otherwise this test will fail.

vite/playground/lib/__tests__/lib.spec.ts

Lines 42 to 49 in 22bd67d

	test('restrisct-helpers-injection', async () => {
	const code = readFile(
	'dist/helpers-injection/my-lib-custom-filename.iife.js',
	)
	expect(code).toMatch(
	`'"use strict"; return (' + expressionSyntax + ").constructor;"`,
	)
	})

This fix relies on the fact that evanw/esbuild#3322 is fixed. But because that fix landed in 0.19.3, we cannot backport this fix to v4 directly.

We can use /(const|var)\s+\S+\s*=\s*function\([^()]*\)\s*\{[\s\w,;]*"use strict";/ instead of this regex to allow var _a, _b part that might be injected by esbuild. But I guess it's safer to simply revert #14094 for v4.