[otlp-transformer] reduce public API surface

[pichlermarc]

Description

The @opentelemetry/otlp-transformer package contains utilities to serialize signals data to and from OTLP (binary protobuf) or OTLP (json). As all OTLP exporters depend on this package, stabilization of @opentelemetry/otlp-transformer is required for OTLP exporter stability.

The API surface currently consists of 40+ types and functions. Reducing the API surface is required to enable optimizations in the serialization process in terms memory use, performance, and bundle size without being constrained by a large stable public API.

Goal of this issue is to:

Move the full serialization process to @opentelemetry/otlp-transformer, this way we will be able to reduce the API surface to:

• an ISerializer interface
• one serializer implementation per signal (metrics, logs, traces) and type (binary protobuf, json)
• one response type per signal.

[github-actions]

This issue is stale because it has been open 60 days with no activity. Remove stale label or comment or this will be closed in 14 days.

[pichlermarc]

Most usages for the types that will be removed are in tests, I'm working on changing the tests so that they are not used anymore. (the start of that is #5196)

[pichlermarc]

See also open-telemetry/opentelemetry-js-contrib#2565 for a follow-up in contrib to replace usage of types that will be removed by completing this issue.