fix(api): fix unreachable @opentelemetry/api/experimental entry

[legendecas]

Which problem is this PR solving?

@opentelemetry/api/experimental is not reachable for missing files.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Integration test with a separate package verifying the @opentelemetry/api package can be properly imported

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

Merging #4446 (09d8767) into main (c98a5d3) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4446   +/-   ##
=======================================
  Coverage   92.38%   92.38%           
=======================================
  Files         331      331           
  Lines        9518     9518           
  Branches     2022     2022           
=======================================
  Hits         8793     8793           
  Misses        725      725           

[pichlermarc]

Thanks for working on this 👍
I like the idea of having some integration tests to test things like that.