feat(otlp-transformer)!: introduce separate entry-points for OTLP serializers

[pichlermarc]

Which problem is this PR solving?

This is the second-to-last breaking PR for @opentelemetry/otlp-transformer before marking the package as stable (#4582). This solves some issues with rollup, that warns even for code that is dead in the end-user's app. See #5096, #4987.

This PR adds entry points for each signal, each signal gets an entry point for protobuf and json to address #5096 and #4987

The new entrypoint structure is:
- /signal, /signal/protobuf, signal/json
- experimental signals are prefixed by experimental/ to allow us marking the package stable before the experimental signals are - the spec moves quicker than we do, so I expect there to always be one that is not stable

Closes #5216
Closes #4584
Fixes #5096
Partially addresses #4987

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

• Unit tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.14%. Comparing base (3fc7170) to head (5b09076).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5263      +/-   ##
==========================================
- Coverage   95.15%   95.14%   -0.02%     
==========================================
  Files         316      316              
  Lines        9166     9166              
  Branches     2023     2023              
==========================================
- Hits         8722     8721       -1     
- Misses        444      445       +1     

Files with missing lines	Coverage Δ
...ges/exporter-logs-otlp-grpc/src/OTLPLogExporter.ts	100.00% <100.00%> (ø)
...ogs-otlp-http/src/platform/node/OTLPLogExporter.ts	100.00% <100.00%> (ø)
...gs-otlp-proto/src/platform/node/OTLPLogExporter.ts	100.00% <100.00%> (ø)
.../exporter-trace-otlp-grpc/src/OTLPTraceExporter.ts	100.00% <100.00%> (ø)
...e-otlp-http/src/platform/node/OTLPTraceExporter.ts	100.00% <100.00%> (ø)
...-otlp-proto/src/platform/node/OTLPTraceExporter.ts	100.00% <100.00%> (ø)
...porter-metrics-otlp-grpc/src/OTLPMetricExporter.ts	100.00% <100.00%> (ø)
...-otlp-http/src/platform/node/OTLPMetricExporter.ts	100.00% <100.00%> (ø)
...otlp-proto/src/platform/node/OTLPMetricExporter.ts	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[chancancode]

Looks good other than the legacy typesVersions thing

[Meligy]

Hello. Any idea when this might be merged and released please?

I suspect it might unblock using the package in nextJS middleware, which runs on Edge runtime, if it's enough for #4987.

[pichlermarc]

Hello. Any idea when this might be merged and released please?

I suspect it might unblock using the package in nextJS middleware, which runs on Edge runtime, if it's enough for #4987.

I'm still waiting on @open-telemetry/javascript-approvers reviews. Once I have an approving review this can get merged. If that happens before Feb 17, we'll release it then.

[david-luna]

nit: I'm not aware off all the history behind logs. I know the API is still experimental. Is that the reason why the word appears in the export path?
@opentelemetry/otlp-transformer package is already experimental so IMHO it feels redundant.

[pichlermarc]

It would unblock us from marking this package as stable before logs becomes stable.
I suppose this will become dependent on the outcome of open-telemetry/opentelemetry.io#8208