Blocks the implementation issue. This one is about stepping through the deep linking workflow, and identifying the points which consumers will need to be able to hook in, thus forming the shape of the API in core_ltix.

Once we have that documented clearly, we can work on the changes both in core_ltix (where we'll put the scaffolding up for the api) and eventually in mod_lti (which will implement it).

Some notes to consider during discovery + design:

1. Needs to consider how components will initiate a deep linking launch (using the modal)
2. Must consider the component-specific parsing of content item returns (mod_lti currently does this when processing a content item)
3. It would be great if we also identified any mod_lti code that can be moved up to core_ltix to facilitate the above (e.g. any part of the content picker modal)

For reference (might help with deeper understanding of Deep Linking in general):
https://www.imsglobal.org/spec/lti-dl/v2p0