Update experimental tag on examples, tests, experimental docs

[mattwthompson]

Description

With the 0.4.0 release, some methods are no longer "experimental" but many tests were not updated and INTERCHANGE_EXPERIMENTAL=1 was unnecessarily set.

This change also moves around an example that's no longer "experimental" into the root directory, which is needed for discovery in the docs automation: openforcefield/openff-docs#71

Checklist

• Add tests
• Lint
• Update docstrings

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.38%. Comparing base (447743c) to head (166c45c).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1150   +/-   ##
=======================================
  Coverage   93.38%   93.38%           
=======================================
  Files          70       70           
  Lines        6036     6036           
=======================================
  Hits         5637     5637           
  Misses        399      399           

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[mattwthompson]

As this intersects with how openff-docs discovers examples, I think @Yoshanuikabundi is the best person to reason through these changes - particularly the example(s) moving around

[j-wags]

This looks good to me. I'm self-assigning and approving since this is such a big blocker, and @Yoshanuikabundi has a hot deadline with the PTM notebook and then BeSMARTS documentation immediately after while we still have Trevor available. If there's a chance that this borks the interface with docs, then let's add a ticket to the backlog to check that once @Yoshanuikabundi has availability again.

[mattwthompson]

Thank you!