Reuse dictionaries in `ActivityExtensions`, `MetricItemExtensions` and `OtlpLogExporter`

[paulomorgado]

Fixes #4943

I have to admit I don't know enough of the usage to know if this is really the best option, but it will reduce the number of allocations and dictionary internal growths.

Changes

Tries to use a single instance of a dictionary for ActivityExtensions, MetricItemExtensions and OtlpLogExporter.

Merge requirement checklist

• [x] CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• [x] Unit tests added/updated
• [x] Appropriate CHANGELOG.md files updated for non-trivial changes
• [x] Changes in public API reviewed (if applicable)

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• :white_check_mark: login: paulomorgado / name: Paulo Morgado (f989e01ea83c120c51b8ebe054702d9beed972d0)

[cijothomas]

@paulomorgado Thanks!. Could you check the benchmarks and share the results here : https://github.com/open-telemetry/opentelemetry-dotnet/tree/main/test/Benchmarks/Exporter so we can see before/after!

[paulomorgado]

@cijothomas,

@paulomorgado Thanks!. Could you check the benchmarks and share the results here : https://github.com/open-telemetry/opentelemetry-dotnet/tree/main/test/Benchmarks/Exporter so we can see before/after!

I've collected the benchmark results. They're a lot.

Are you looking for any particular ones?

[cijothomas]

@cijothomas,

@paulomorgado Thanks!. Could you check the benchmarks and share the results here : https://github.com/open-telemetry/opentelemetry-dotnet/tree/main/test/Benchmarks/Exporter so we can see before/after!

I've collected the benchmark results. They're a lot.

Are you looking for any particular ones?

Could you share, so it is easy to tell how much we are improving? (also ensures we don't accidentally regress!) Example : https://github.com/open-telemetry/opentelemetry-dotnet/pull/5457#issuecomment-2008107292

There are few OTLPExporter specific benchmarks: https://github.com/open-telemetry/opentelemetry-dotnet/blob/main/test/Benchmarks/Exporter/OtlpTraceExporterBenchmarks.cs

[vishweshbankwar]

@paulomorgado - Thank you for your time, appreciate the help. As discussed https://github.com/open-telemetry/opentelemetry-dotnet/pull/5727#discussion_r1661310935, I am closing this PR as the implementation is soon going to change.