implement basic Java 8 lambda support

The two big pieces here are basic invokedynamic support and a working
version of LambdaMetaFactory.metafactory.  The latter works by
dynamically building a synthetic class with three methods: a static
factory method, a constructor for the factory method to call, and a
method to satisfy the requested interface which defers to the
specified MethodHandle.

This work relies heavily on Avian's specific MethodType and
MethodHandle implementations, which provide extra, non-standard
features to make code generation easier.  That means we'll probably
need to use Avian's versions of java.lang.invoke.* even when building
with the OpenJDK or Android class libraries.

classpath/java/lang/reflect/Method.java

@@ -18,7 +18,7 @@ import avian.Classes;
 import java.lang.annotation.Annotation;
 
 public class Method<T> extends AccessibleObject implements Member {
-  private final VMMethod vmMethod;
+  public final VMMethod vmMethod;
   private boolean accessible;
 
   public Method(VMMethod vmMethod) {
@@ -59,6 +59,18 @@ public class Method<T> extends AccessibleObject implements Member {
     return getSpec(vmMethod);
   }
 
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    if (vmMethod.class_ != null) {
+      sb.append(Classes.makeString(vmMethod.class_.name, 0,
+                                   vmMethod.class_.name.length - 1));
+      sb.append(".");
+    }
+    sb.append(getName());
+    sb.append(getSpec());
+    return sb.toString();
+  }
+  
   public static String getSpec(VMMethod vmMethod) {
     return Classes.makeString(vmMethod.spec, 0, vmMethod.spec.length - 1);
   }