Revert pattern to folder export

[lukastaegert]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:
Reverts #3896

Description

As I did not realize, #3896 was a breaking change as it prevented extension-less requires for nested files. This reverts this change.

[rollup-bot]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#revert-exports-change

or load it into the REPL:
https://rollupjs.org/repl/?circleci=13792

[codecov]

Codecov Report

Merging #3898 (5a25161) into master (8eafd72) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3898   +/-   ##
=======================================
  Coverage   97.07%   97.07%           
=======================================
  Files         187      187           
  Lines        6538     6538           
  Branches     1901     1901           
=======================================
  Hits         6347     6347           
  Misses        101      101           
  Partials       90       90           

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