Define how SDK implements Tracer.Enabled (#4537)

Fixes
#4397

Towards
#4463

Content is based on
https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/sdk.md#enabled.

---------

Co-authored-by: Carlos Alberto Cortez <calberto.cortez@gmail.com>

Author: pellared

CHANGELOG.md

@@ -11,6 +11,9 @@ release.
 
 ### Traces
 
+- Define how SDK implements `Tracer.Enabled`.
+  ([#4537](https://github.com/open-telemetry/opentelemetry-specification/pull/4537))
+
 ### Metrics
 
 ### Logs

specification/logs/sdk.md

@@ -202,7 +202,7 @@ the implementation SHOULD set it equal to the current time.
 
 **Status**: [Development](../document-status.md)
 
-`Enabled` MUST return `false` when:
+`Enabled` MUST return `false` when either:
 
 - there are no registered [`LogRecordProcessors`](#logrecordprocessor),
 - `Logger` is disabled ([`LoggerConfig.disabled`](#loggerconfig) is `true`),

specification/trace/sdk.md

@@ -19,6 +19,7 @@ linkTitle: SDK
   * [ForceFlush](#forceflush)
 - [Tracer](#tracer)
   * [TracerConfig](#tracerconfig)
+  * [Enabled](#enabled)
 - [Additional Span Interfaces](#additional-span-interfaces)
 - [Sampling](#sampling)
   * [Recording Sampled reaction table](#recording-sampled-reaction-table)
@@ -199,6 +200,18 @@ It consists of the following parameters:
   necessary for implementations to ensure that changes to `disabled` are
   immediately visible to callers of `Enabled`.
 
+### Enabled
+
+**Status**: [Development](../document-status.md)
+
+`Enabled` MUST return `false` when either:
+
+- there are no registered [`SpanProcessors`](#span-processor),
+- `Tracer` is disabled ([`TracerConfig.disabled`](#tracerconfig) is `true`).
+
+Otherwise, it SHOULD return `true`.
+It MAY return `false` to support additional optimizations and features.
+
 ## Additional Span Interfaces
 
 The [API-level definition for Span's interface](api.md#span-operations)