Publish Segment.size and Segment.remainingCapacity (#409)

Fixes #408

Author: fzhinkin

core/api/kotlinx-io-core.api

@@ -111,8 +111,8 @@ public final class kotlinx/io/Segment {
 	public final synthetic fun getNext ()Lkotlinx/io/Segment;
 	public final synthetic fun getPos ()I
 	public final synthetic fun getPrev ()Lkotlinx/io/Segment;
-	public final synthetic fun getRemainingCapacity ()I
-	public final synthetic fun getSize ()I
+	public final fun getRemainingCapacity ()I
+	public final fun getSize ()I
 	public final synthetic fun setLimit (I)V
 	public final synthetic fun setNext (Lkotlinx/io/Segment;)V
 	public final synthetic fun setPos (I)V

core/common/src/Segment.kt

@@ -345,14 +345,20 @@ public class Segment {
         limit += srcEndOffset - srcStartOffset
     }
 
-    @PublishedApi
-    @get:JvmSynthetic
-    internal val size: Int
+    /**
+     * The number of readable bytes contained in this segment.
+     *
+     * @sample kotlinx.io.samples.unsafe.UnsafeBufferOperationsSamples.readUleb128
+     */
+    public val size: Int
         get() = limit - pos
 
-    @PublishedApi
-    @get:JvmSynthetic
-    internal val remainingCapacity: Int
+    /**
+     * The number of bytes that could be written into this segment.
+     *
+     * @sample kotlinx.io.samples.unsafe.UnsafeBufferOperationsSamples.writeUleb128Array
+     */
+    public val remainingCapacity: Int
         get() = data.size - limit
 
     /**