improvement: Add most of missing JDK9+ methods for java.nio buffers (…

…scala-native#3681)

* Fix accessing mapped byte buffers if offset is not page alligned
* Use template to define base java nio buffer types
* Add JDK13 method Buffer.slice(Int,Int)
* Add absolute bulk offset get/put methods
* Add tests for alignment offsets/slices
* Move ALL java.nio buffer tests to require-jdk16 subdir due to problems with decoupling BufferAdapters for API introduced in JDK9+
* Fix build, move remaining buffer tests to required-jdk16 sources, exclude them in Build def

javalib/src/main/scala/java/nio/Buffer.scala

@@ -92,8 +92,12 @@ abstract class Buffer private[nio] (val _capacity: Int) {
 
   def isDirect(): Boolean
 
+  // Since JDK 9
   def slice(): Buffer
+  // Since JDK 13
+  def slice(index: Int, length: Int): Buffer
 
+  // Since JDK 9
   def duplicate(): Buffer
 
   override def toString(): String =
@@ -124,6 +128,15 @@ abstract class Buffer private[nio] (val _capacity: Int) {
   // PointerByteBuffer specific
   private[nio] def _rawDataPointer: unsafe.Ptr[Byte] = null
 
+  private[nio] def address: unsafe.Ptr[Byte] =
+    if (_rawDataPointer != null) _rawDataPointer
+    else if (_mappedData != null) _mappedData.data
+    else
+      _array
+        .asInstanceOf[scalanative.runtime.Array[_]]
+        .atUnsafe(_offset)
+        .asInstanceOf[unsafe.Ptr[Byte]]
+
   // HeapByteBuffer specific
   private[nio] def _byteArray: Array[Byte] =
     throw new UnsupportedOperationException