Add isolating log record processor (#4062)

## Why

Fixes #4010 (read the issue for more details)

The SDK SHOULD offer a way to make independent log processing. I find it
as a missing feature that should be covered by by the specification.

## What

This PR tries to achieve it in the following way:
- SDK SHOULD provide an isolating processor allowing independent log
processing pipelines. Source:
#4010 (comment)

This approach should be solving the issue at least for Java, .NET,
Python, JavaScript, Go. This proposal should not make any existing log
SDKs not compliant with the specification.

I think that the same approach could be also adopted in tracing for span
processors (but I have not yet investigated it in depth).

## Remarks

I created a separate issue for specifying whether (by default) a change
to a record made in a processor is propagated to next registered
processor. See
#4065

CHANGELOG.md

@@ -15,6 +15,9 @@ release.
 
 ### Logs
 
+- Add the in-development isolating log record processor.
+  ([#4062](https://github.com/open-telemetry/opentelemetry-specification/pull/4062))
+
 ### Events
 
 ### Resource

specification/logs/sdk.md

@@ -28,6 +28,7 @@
   * [Built-in processors](#built-in-processors)
     + [Simple processor](#simple-processor)
     + [Batching processor](#batching-processor)
+    + [Isolating processor](#isolating-processor)
 - [LogRecordExporter](#logrecordexporter)
   * [LogRecordExporter operations](#logrecordexporter-operations)
     + [Export](#export)
@@ -372,7 +373,13 @@ make the flush timeout configurable.
 ### Built-in processors
 
 The standard OpenTelemetry SDK MUST implement both simple and batch processors,
-as described below. Other common processing scenarios SHOULD be first considered
+as described below.
+
+**Status**: [Development](../document-status.md) -
+The standard OpenTelemetry SDK SHOULD implement an isolating processor,
+as described below.
+
+Other common processing scenarios SHOULD be first considered
 for implementation out-of-process
 in [OpenTelemetry Collector](../overview.md#collector).
 
@@ -405,6 +412,21 @@ representations to the configured `LogRecordExporter`.
 * `maxExportBatchSize` - the maximum batch size of every export. It must be
   smaller or equal to `maxQueueSize`. The default value is `512`.
 
+#### Isolating processor
+
+**Status**: [Development](../document-status.md)
+
+This is an implementation of `LogRecordProcessor` ensuring the log record
+passed to `OnEmit` of the configured `processor` does not share mutable data
+with subsequent registered processors.
+For example, the `OnEmit` implementation of the isolating processor can be
+a decorator that makes a deep copy of the log record before passing it to
+the configured `processor`.
+
+**Configurable parameters:**
+
+* `processor` - processor to be isolated.
+
 ## LogRecordExporter
 
 `LogRecordExporter` defines the interface that protocol-specific exporters must