Move otlp utilities to otlp package

[jack-berg]

Related to #6970

We have a bunch of public classes in internal packages in opentelemetry-exporter-common which are only used in opentelemetry-exporter-otlp (and the unpublished opentelemetry-exporter-profiles).

Moving these public classes to where they are used reduces shared internal code.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.27%. Comparing base (fdb8194) to head (f4b71c1).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8326   +/-   ##
=========================================
  Coverage     90.27%   90.27%           
- Complexity     7693     7695    +2     
=========================================
  Files           850      851    +1     
  Lines         23207    23209    +2     
  Branches       2356     2356           
=========================================
+ Hits          20951    20953    +2     
  Misses         1530     1530           
  Partials        726      726           

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