Support out of proc Histogram Base 2 Exponential aggregation

[tarekgh]

Fixes #109388

This change introduces support for out-of-process histograms using base-2 exponential aggregation.

• Aggregation is implemented according to the OpenTelemetry specification, with the calculation logic ported from the opentelemetry-dotnet project.
• Negative values are currently ignored during recording, in line with the current specification. Support for negative values can be added in the future if needed.
• A configuration option has been added to the event source, allowing base-2 exponential aggregation to be set as the default histogram aggregation method. In the future, per-meter or per-instrument aggregation settings can be introduced based on user feedback.

[Copilot]

Pull Request Overview

This PR introduces support for out‑of‑process histograms using Base‑2 exponential aggregation, in accordance with the OpenTelemetry spec. Key changes include adding the new Base2ExponentialHistogramAggregator and CircularBufferBuckets classes, extending configuration options in the event source and aggregation manager, and adding tests to validate the new histogram behavior.

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
System.Diagnostics.DiagnosticSource.Tests.csproj	Added compile links for new aggregator and buckets test files.
tests/Resources/Strings.resx	Added error messages for invalid histogram configuration values.
MetricEventSourceTests.cs	Introduced new tests verifying Base‑2 histogram aggregation with various recordings.
MetricsEventSource.cs	Added event and parsing logic for Base‑2 exponential histogram aggregation.
CircularBufferBuckets.cs	New circular buffer implementation for bucket counting in histograms.
Base2ExponentialHistogramAggregator.cs	New aggregator implementation for Base‑2 exponential histograms; updates measurement and supports scale reduction.
AggregationManager.cs	Updated to select the appropriate aggregator based on histogram aggregation configuration.
Other files	Updated project files, resource strings, and third‑party notices accordingly.

[tarekgh]

/azp run runtime-libraries-coreclr outerloop

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Azure Pipelines successfully started running 1 pipeline(s).

[tarekgh]

CC @reyang as I ported some code originally written by him.

[tarekgh]

/azp run runtime-libraries-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[noahfalk]

A few suggestions/questions inline. LGTM overall. I didn't scrutinize the algorithm for the histogram itself as I assume that is copied code and appears well tested.

[tarekgh]

/azp run runtime-libraries-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[tarekgh]

/azp run runtime-libraries-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[tarekgh]

/azp run runtime-libraries-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).