This changes the Log Emitter to run the `consumerFunc`
on the whole batch, instead of splitting the batch into individual entries
and calling `consumerFunc` on each of them.

This doesn't change much while the Log Emitter has its own `batch` buffer,
but if we remove the `batch` buffer (see open-telemetry#35456),
this should prevent the performance drop described in open-telemetry#35454.

This changes the Log Emitter to run the `consumerFunc`
on the whole batch, instead of splitting the batch into individual entries
and calling `consumerFunc` on each of them.

This doesn't change much while the Log Emitter has its own `batch` buffer,
but if we remove the `batch` buffer (see open-telemetry#35456),
this should prevent the performance drop described in open-telemetry#35454.

This changes the Log Emitter to run the `consumerFunc`
on the whole batch, instead of splitting the batch into individual entries
and calling `consumerFunc` on each of them.

This doesn't change much while the Log Emitter has its own `batch` buffer,
but if we remove the `batch` buffer (see open-telemetry#35456),
this should prevent the performance drop described in open-telemetry#35454.

Related to open-telemetry#38054.

The File Log receiver benchmark has a scope that is larger than both
the [FIle consumer benchmark](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/fileconsumer/benchmark_test.go)
and the [File input benchmark](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/operator/input/file/benchmark_test.go).
Compared to the File input benchmark, the File Log receiver benchmark includes:
- translating of Stanza entries to pdata logs ([converter.ConvertEntries](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/adapter/converter.go#L20)).
- batching of logs in [LogEmitter](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/operator/helper/emitter.go#L103).

This new benchmark should be useful when comparing performance with and without batching in LogEmitter,
see open-telemetry#35456.

…38171)

#### Description

Related to
#38054.

The File Log receiver benchmark has a scope that is larger than both the
[File consumer
benchmark](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/fileconsumer/benchmark_test.go)
and the [File input
benchmark](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/operator/input/file/benchmark_test.go).
Compared to the File input benchmark, the scope of File Log receiver
benchmark includes:
- translating of Stanza entries to pdata logs
([converter.ConvertEntries](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/adapter/converter.go#L20)).
- batching of logs in
[LogEmitter](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/operator/helper/emitter.go#L103).

This new benchmark should help us measure the performance impact of
[removing batching from
LogEmitter](#35456)
after it is [added in File
consumer](#35455).

#### Link to tracking issue

- Needed for
#35456

#### Description

Removes batching in LogEmitter to prevent data loss during ungraceful
shutdown of the collector. See
#35456
for details.

This is done behind a feature gate, as it may have a negative
performance impact, depending on user configuration. See the added
documentation for the feature gate.

On implementation side, this was done by renaming the existing
`LogEmitter` struct to `BatchingLogEmitter` and introducing a new
`SynchronousLogEmitter`, see `pkg/stanza/adapter/emitter.go`.

#### Link to tracking issue

- Fixes
#35456

#### Testing

Added unit tests in `pkg/stanza/adapter/emitter_test.go`.

Adapted the benchmarks `pkg/stanza/adapter/receiver_test.go` to run for
both the existing BatchingLogEmitter and the new SynchronousLogEmitter.

#### Documentation

Added documentation for the feature gate.