Motivation:
Composite buffers are uniquely positioned to be able to extend their underlying storage relatively cheaply.
This fact is relied upon in a couple of buffer use cases within Netty, that we wish to support.
Modification:
Add a static `extend` method to Allocator, so that the CompositeBuf class can remain internal.
The `extend` method inserts the extension buffer at the end of the composite buffer as if it had been included from the start.
This involves checking offsets and byte order invariants.
We also require that the composite buffer be in an owned state.
Result:
It's now possible to extend a composite buffer with a specific buffer, after the composite buffer has been created.
236097e081