[BUG] [Java] Memory leak due to table writers never being destroyed after done writing

For all kinds of table writers (Java code: `Table.java`, JNI code: `TableJni.cpp`), the native C++ instances are never destroyed after calling `close()` in the corresponding Java classes. For example:
```
@Override
public void close() throws CudfException {
if (writerHandle != 0) {
writeParquetEnd(writerHandle);
}
writerHandle = 0;
```

And here is the C++ function `writeParquetEnd`:
```
try {
cudf::jni::auto_set_device(env);
state->writer->close();
}
```

Note that `state` is an unmanaged pointer that corresponds to `writerHandle` in Java and stores `writer` as a `unique_ptr`. So the `writer` instance is destroyed automatically when `state` is destroyed, however, `state` is never destroyed.

When `writeParquetEnd` is called, the C++ code only calls the member `close()` function of the writer, never calls `delete` on the `state` instance. After this, the Java code simply leaves that native instance dangled.