Add methods to NetSocket for buffer handling

Using Vertx 4.2.7 currently.

Please add `getWriteQueueSize`. While `writeQueueFull` is useful, it would be helpful to see what the current write queue size used to calculate `writeQueueFull` is so we can offer multi-tiered escalation for back pressure handling instead of just full or not full. E.g., in a video stream pipe, can vary the quality based on different levels of backlog determined by the current write queue size.

Please add a public `getWriteQueueMaxSize`. There is currently a `setWriteQueueMaxSize` method with no corresponding getter. It would be useful to see what the current value is before changing it in pipeline handlers.