[asm-cherry-pick] Use MethodWriter to compute maxLocals / maxStack

Make class MethodWriter public and add accessors for maxLocals and
maxStack. This is the simplest way to compute the maxs using the
ASM framework. It is used in the optimizer, see
scala/scala@90781e8

TODO: this should no longer be necessary since
scala/scala#4811

Originally added in
lrytz/scala@91810c9

Author: lrytz

src/main/java/scala/tools/asm/MethodWriter.java

@@ -36,7 +36,7 @@
  * @author Eric Bruneton
  * @author Eugene Kuleshov
  */
-final class MethodWriter extends MethodVisitor {
+public final class MethodWriter extends MethodVisitor {
 
   /** Indicates that nothing must be computed. */
   static final int COMPUTE_NOTHING = 0;
@@ -312,9 +312,17 @@ final class MethodWriter extends MethodVisitor {
   /** The max_stack field of the Code attribute. */
   private int maxStack;
 
+  public int getMaxStack() {
+      return maxStack;
+  }
+
   /** The max_locals field of the Code attribute. */
   private int maxLocals;
 
+  public int getMaxLocals() {
+      return maxLocals;
+  }
+
   /** The 'code' field of the Code attribute. */
   private final ByteVector code = new ByteVector();