Deprecate Resource.writeTo(OutputStream, long, long)

[joakime]

Based on a review of PR #3923 it was identified that the entire writing of Resources and HttpContent is a bit hairy with a lot of similar code and apparent code duplication.

In order to simplify things, it was decided that Resource.writeTo(OutputStream, long, long) should be deprecated in Jetty 9.4.x and removed in Jetty 10.0.x

It was proposed by @sbordet that the writing of content should be handled somewhere at the HttpContent level, perhaps as a jetty-io (or even a jetty-server) feature.

Some of the brainstormed possible interfaces for HttpContent were ...

// Whole content send
HttpContent.send(Channel, Callback);

// Range content send - simple / single range
HttpContent.send(Channel, long start, long length, Callback);

// Range content send - smart / multiple ranges
HttpContent.send(MultiPartOutputStream, InclusiveByteRanges, Callback);