Cannot forcefully include core-js polyfill esnext.*

## Bug Report

- [ ] I would like to work on a fix!

**Current behavior**

I'd like to include certain stage-x core-js polyfills, e.g. `esnext.aggregate-error` (stage 4) or `esnext.symbol.observable`. I specify these in the `include` option, and I've also tried to import `core-js/modules/esnext.aggregate-error` manually. No error is thrown by Babel. But Babel doesn't just not include the import when expanding the `core-js` import, it actively _removes_ the explicit import, meaning there doesn't seem to be _any_ way to include a stage-4 polyfill in an application.

**Input Code**

```js
import 'core-js'
```

```js
import 'core-js'

import 'core-js/modules/esnext.aggregate-error'

const error = new AggregateError()
```

**Expected behavior**

One of these two ways should result in this import in the output file:

```js
import 'core-js/modules/esnext.aggregate-error'
```

**Babel Configuration (babel.config.js, .babelrc, package.json#babel, cli command, .eslintrc)**
- Filename: `babel.config.js`

```js
[
'@babel/preset-env',
{
useBuiltIns: 'entry',
include: [
'esnext.symbol.observable',
'esnext.aggregate-error',
],
corejs: 3,
},
```

**Environment**

```
System:
OS: macOS 10.15.5
Binaries:
Node: 14.5.0 - ~/.local/share/powershell/Modules/nvm/2.4.0/vs/v14.5.0/bin/node
Yarn: 1.13.0 - /usr/local/bin/yarn
npm: 6.13.4 - ~/git/sourcegraph/node_modules/.bin/npm
npmPackages:
@babel/core: ^7.10.5 => 7.10.5
@babel/preset-env: ^7.10.4 => 7.10.4
```

Start with the babel.config.js configuration and reproduce both import examples using @babel/preset-env with useBuiltIns: "entry", corejs: 3, and the listed include values. Trace how Babel handles the core-js import and explicit esnext.aggregate-error import; done means the expected core-js/modules/esnext.aggregate-error import remains in the output.

Written by the indexing model from the issue text.