Support j.l.i.BoundMethodHandle$Species_* classes unloading

BMH$Species_* classes are loaded using bootstrap class loader and hence can't be GCed.

src/java.base/share/classes/java/lang/invoke/BoundMethodHandle.java:
            // load class
            final byte[] classFile = cw.toByteArray();
            InvokerBytecodeGenerator.maybeDump(className, classFile);
            Class<? extends BoundMethodHandle> bmhClass =
                //UNSAFE.defineAnonymousClass(BoundMethodHandle.class, classFile, null).asSubclass(BoundMethodHandle.class);
                UNSAFE.defineClass(className, classFile, 0, classFile.length,
                                   BoundMethodHandle.class.getClassLoader(), null)
                    .asSubclass(BoundMethodHandle.class);

Consider moving to VM anonymous classes instead. It means all references to Species_* field accessors in LambdaForms should be through method handles and not symbolic references.