Change default buffer size to be 8K (same default as in java BufferedReader).

Rename internal constants.

libraries/stdlib/src/kotlin/io/Constants.kt

@@ -5,14 +5,13 @@ package kotlin.io
 /**
  * Returns the default buffer size when working with buffered streams.
 */
-
-public const val DEFAULT_BUFFER_SIZE: Int = 64 * 1024
+public const val DEFAULT_BUFFER_SIZE: Int = 8 * 1024
 
 /**
  * Returns the default block size for forEachBlock().
  */
-internal const val defaultBlockSize: Int = 4096
+internal const val DEFAULT_BLOCK_SIZE: Int = 4096
 /**
  * Returns the minimum block size for forEachBlock().
  */
-internal const val minimumBlockSize: Int = 512
+internal const val MINIMUM_BLOCK_SIZE: Int = 512

libraries/stdlib/src/kotlin/io/FileReadWrite.kt

@@ -102,7 +102,7 @@ public fun File.appendText(text: String, charset: Charset = Charsets.UTF_8): Uni
  *
  * @param action function to process file blocks.
  */
-public fun File.forEachBlock(action: (ByteArray, Int) -> Unit): Unit = forEachBlock(defaultBlockSize, action)
+public fun File.forEachBlock(action: (ByteArray, Int) -> Unit): Unit = forEachBlock(DEFAULT_BLOCK_SIZE, action)
 
 /**
  * Reads file by byte blocks and calls [action] for each block read.
@@ -114,7 +114,7 @@ public fun File.forEachBlock(action: (ByteArray, Int) -> Unit): Unit = forEachBl
  * @param blockSize size of a block, replaced by 512 if it's less, 4096 by default.
  */
 public fun File.forEachBlock(blockSize: Int, action: (ByteArray, Int) -> Unit): Unit {
-    val arr = ByteArray(if (blockSize < minimumBlockSize) minimumBlockSize else blockSize)
+    val arr = ByteArray(blockSize.coerceAtLeast(MINIMUM_BLOCK_SIZE))
     val fis = FileInputStream(this)
 
     try {