Add ability to exclude polyfills for a certain section of code

From https://github.com/babel/babel-polyfills/issues/10#issuecomment-623128674 (@pleunv)

> I also suspect (but haven't confirmed) that when a dependency does feature detection with a slow path fallback or provides an inline poly/ponyfill themselves it still includes a polyfill on babel's side. Cases like that you really want to avoid.

Start by reading the linked issue #10 discussion and its referenced comment to understand the proposed scoped exclusion behavior. Identify the project entry points and tests for polyfill injection, then define completion as a reproducible way to exclude polyfills for a selected code section without losing required behavior.

Written by the indexing model from the issue text.