SSE Support

[thecodedrift]

Taskless loaders only work over HTTP with standard fetch lifecycle events. This isn't compatible with server-sent-events, which need support for streaming payloads.

Known TODOs:

• Support an event type beyond pre/post that is optional. Working name event which receives a server sent event
• Add try/catch for methods that may not exist in the Pack or expose method capabilities in the manifest, preferably the later
• There may be additional plumbing required to support

This will be edited if more work is discovered.

Prior History:

• https://github.com/Azure/fetch-event-source - also MIT licensed and their parse infrastructure may be suitable out of the box
• https://developer.mozilla.org/en-US/docs/Web/API/Streams_API/Using_readable_streams - the underlying APIs fetch-event-source is using