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 🥂 !