Clarification on debug output

Hi,

I'm experimenting with the `usage-pure` mode to polyfill. The debug output from the plugins seems to indicate that no polyfills are applied - every source file has a debug output of:
`Based on your code and targets, the corejs3 polyfill did not add any polyfill.`
`Based on your code and targets, the regenerator polyfill did not add any polyfill.`

However, when I look at the output JS, I can see that polyfills (such as Promise) have been applied (as I would expect). How come none of the applied polyfills are mentioned in the debug output? Am I missing them being applied elsewhere or is this a quirk of the new polyfills plugins? Thanks!

For information:
I have a browserslist config in package.json of `> 0.25%, not dead`, which gives a targets list of:

```
Using targets: {
"chrome": "85",
"edge": "88",
"firefox": "85",
"ie": "11",
"ios": "12.2",
"opera": "73",
"safari": "13.1",
"samsung": "13"
}
```

My Babel config looks like this:

```
{
"presets": [
[
"@babel/typescript",
{
"jsxPragma": "h"
}
],
[
"@babel/preset-env",
{
"useBuiltIns": false,
//"modules": false,
"bugfixes": true,
"debug": true
}
]
],
"plugins": [
"@babel/proposal-class-properties",
"@babel/proposal-object-rest-spread",
[
"@babel/plugin-transform-react-jsx",
{
"pragma": "h",
"pragmaFrag": "Fragment"
}
],
[
"babel-plugin-transform-builtin-extend",
{
"globals": ["Error"]
}
],
[
"@babel/transform-runtime",
{
"regenerator": false,
"debug": true
}
],
["polyfill-corejs3", {
"method": "usage-pure",
"debug": true
}],
["polyfill-regenerator", {
"method": "usage-pure",
"debug": true
}]
]
}
```

Reproduce the reported behavior using the package.json Browserslist targets and the Babel configuration shown, especially the usage-pure corejs3 and regenerator plugins. Compare their debug messages with the emitted JavaScript and determine whether the discrepancy is expected or indicates missing reporting; done means the behavior is explained or corrected with corresponding coverage.

Written by the indexing model from the issue text.