This PR fixes a bug when using the --experimental-dts.

Let's say we have the following file structure:

// src/shared.ts
export const declare1 = 'declare1'
export const declare2 = 'declare2'

// src/entry1.ts
export { declare1 } from './shared'

// src/entry2.ts
export { declare2 } from './shared'

In this example, entry1.ts and entry2.ts are public entry files. In the generated entry1.d.ts, it should only contain declare1, and entry2.d.ts should only contain declare2. However, the generated entry1.d.ts and entry2.d.ts incorrectly contain both declare1 and declare2.

This PR fixes this bug and adds a test case.