Add since attribute to Deprecated annotation

Introduce the since attribute to the Deprecated annotation to allow
documenting the version or date when an API was marked as deprecated.
Update the KDoc to explain its purpose.

Author: kpavlov

libraries/stdlib/src/kotlin/Annotations.kt

@@ -19,6 +19,7 @@ import kotlin.annotation.AnnotationTarget.*
  * To help removing deprecated API gradually, the property [level] could be used.
  * Usually a gradual phase-out goes through the "warning", then "error", then "hidden" or "removed" stages:
  * - First and by default, [DeprecationLevel.WARNING] is used to notify API consumers, but not to break their compilation or runtime usages.
+ *   You can optionally set the [since] attribute to specify when the deprecation started (e.g., version or date).
  * - Then, some time later the deprecation level is raised to [DeprecationLevel.ERROR], so that no new Kotlin code can be compiled
  *   using the deprecated API.
  * - Finally, the API is either removed entirely, or hidden ([DeprecationLevel.HIDDEN]) from code,
@@ -30,13 +31,17 @@ import kotlin.annotation.AnnotationTarget.*
  *  the deprecated API usage.
  * @property level Specifies how the deprecated element usages are reported in code.
  *  See the [DeprecationLevel] enum for the possible values.
+ * @property since Specifies the version or date when the API element was marked as deprecated.
+ *  This helps API users track deprecations over time and identify the first point in history
+ *  where the deprecation was introduced.
  */
 @Target(CLASS, FUNCTION, PROPERTY, ANNOTATION_CLASS, CONSTRUCTOR, PROPERTY_SETTER, PROPERTY_GETTER, TYPEALIAS)
 @MustBeDocumented
 public annotation class Deprecated(
     val message: String,
     val replaceWith: ReplaceWith = ReplaceWith(""),
-    val level: DeprecationLevel = DeprecationLevel.WARNING
+    val level: DeprecationLevel = DeprecationLevel.WARNING,
+    val since: String = "",
 )
 
 /**