Support stand-alone exponential histogram data structure for use by OpenTelemetry components

[jmacd]

Problem Statement

#2501 describes adding stand-alone exponential histogram mapping functions for use by OpenTelemetry components (e.g., the OTel Collector's standard logging exporter). The same request exists for a stand-alone exponential histogram data structure (e.g., the OTel Collector's statsd receiver).

Proposed Solution

Following the decision in #3169, create a structure sub-package, a sibling of mapping that supports use in the Collector as well as by the metrics SDK. The contents of #3022 contain the pending structure package.

Alternatives

Presently, the pending PR open-telemetry/opentelemetry-collector-contrib#12951 refers to Lightstep's copy of the code in #3022, which is acceptable as a temporary measure. Ideally we do not maintain this dependency indefinitely.

[MrAlias]

Added to the beta milestone. Please remove if this was in error.

[jmacd]

(I was going to ask you first 😁)

[MrAlias]

Yeah, lets add it now than. We can always bump it later if want to re-scope the milestone, but it is good to track it as work that needs to be done for the metric SDK (at some point).

[leonyu879]

How about the progress?