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/Proxy.java

@@ -23,6 +23,7 @@ import avian.ConstantPool;
 import avian.ConstantPool.PoolEntry;
 
 import avian.Assembler;
+import avian.Assembler.FieldData;
 import avian.Assembler.MethodData;
 
 import java.util.List;
@@ -402,6 +403,7 @@ public class Proxy {
     ByteArrayOutputStream out = new ByteArrayOutputStream();
     Assembler.writeClass
       (out, pool, nameIndex, superIndex, interfaceIndexes,
+       new FieldData[0],
        methodTable.toArray(new MethodData[methodTable.size()]));
 
     byte[] classData = out.toByteArray();