Refactor metrics to remove MeterSharedState

[jack-berg]

I'm starting to think about how to allow for updating SDK configuration. Starting with metrics because traces and logs are a cake walk in comparison. While doing some analysis I realized that MeterSharedState is a silly concept - all of its logic and state can just be held directly on the respective SdkMeter.

This reduces complexity and makes it easier to reason over.

[codecov]

Codecov Report

Attention: Patch coverage is 96.92308% with 4 lines in your changes missing coverage. Please review.

Project coverage is 90.47%. Comparing base (e4f3978) to head (5a341ab).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...in/java/io/opentelemetry/sdk/metrics/SdkMeter.java	95.87%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6845      +/-   ##
============================================
- Coverage     90.49%   90.47%   -0.02%     
+ Complexity     6599     6588      -11     
============================================
  Files           731      729       -2     
  Lines         19738    19724      -14     
  Branches       1938     1941       +3     
============================================
- Hits          17862    17846      -16     
- Misses         1285     1286       +1     
- Partials        591      592       +1     

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[jkwatson]

I believe this was a holdover from OC metrics, where (IIRC), you could have more than one meter instance that shared the same state. If we don't need it any more, then 🥂 !