Add arch test to detect usage of shared internal code

[jack-berg]

Related to #6970.

This test prints out instances of shared internal code use. We could eventually remove all the detected instances, at which point we could fail the build instead of just printing.

But there's a long way to go. See this gist for the current state of affairs.

Note: I don't currently have a good way to tell when internal code is referenced for things like the SDK's implementation of of opentelemetry-api-incubating, which is switched to a compile dependency in #6944.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.15%. Comparing base (62049e7) to head (b2eb978).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #6978   +/-   ##
=========================================
  Coverage     90.15%   90.15%           
  Complexity     7476     7476           
=========================================
  Files           836      836           
  Lines         22550    22550           
  Branches       2224     2224           
=========================================
  Hits          20331    20331           
  Misses         1515     1515           
  Partials        704      704           

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[jack-berg]

Resurrecting this and marking ready for review @open-telemetry/java-approvers.

There have been a number of topics coming up lately that reinforce the need to avoid shared internal code. A couple that come to mind:

• Add initial OSGi support #7964 need to export our *.internal.* packages even though we shouldn't. Blocked by Strengthen versioning requirements #6970.
• Deprecate zipkin exporter #7863 need to deprecate and eventually stop publishing zipkin exporter, but before we do, need to make sure its not using any shared internal code so users can continue to use old versions it without the risk of changes to shared internal code breaking it.

[jack-berg]

Here's the TODO list. All these modules use shared internal code.

In contrast, the list of modules which DO NOT use shared internal code is small:

• opentelemetry-common
• opentelemetry-context
• opentelemetry-tracing-shim
• opentelemetry-api
• opentelemetry-extension-kotlin
• opentelemetry-sdk