[sdk-metrics] MetricPoint lookup perf tweaks

[CodeBlanch]

Changes

• Switch LookupAggregatorStore & LookupAggregatorStoreForDeltaWithReclaim to return a ref to the MetricPoint instead of the index to the MetricPoint. For cases where we created a MetricPoint, or reused one in the case of delta reclaim, this saves a second lookup/index/bounds-check into the array before the update is processed.

• Use MemoryMarshal.GetArrayDataReference on TFMs where it is supported to access the zero-tag MetricPoint (index 0) and the overflow MetricPoint (index 1) instead of performing a lookup/index/bounds-check on each measurement where they are used.

• Some renames to help with readability/clarity inside AggregatorStore...

  • LookupAggregatorStore -> LookupMetricPoint
  • LookupAggregatorStoreForDeltaWithReclaim -> LookupMetricPointForDeltaWithReclaim
  • Anything with "CustomTags" in the name now uses "WithTagFilerting" for example UpdateDoubleCustomTags -> UpdateDoubleWithTagFiltering

Benchmarks

TODO

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)

[codecov]

Codecov Report

Attention: Patch coverage is 82.51748% with 25 lines in your changes missing coverage. Please review.

Project coverage is 86.22%. Comparing base (6250307) to head (6165854).
Report is 353 commits behind head on main.

Files with missing lines	Patch %	Lines
src/OpenTelemetry/Metrics/AggregatorStore.cs	82.51%	25 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5869      +/-   ##
==========================================
+ Coverage   83.38%   86.22%   +2.84%     
==========================================
  Files         297      257      -40     
  Lines       12531    11220    -1311     
==========================================
- Hits        10449     9675     -774     
+ Misses       2082     1545     -537     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	86.18% <82.51%> (?)
unittests-Project-Stable	86.11% <78.32%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/OpenTelemetry/Metrics/AggregatorStore.cs	85.99% <82.51%> (+5.60%)	⬆️

... and 232 files with indirect coverage changes

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