Stop using Vuex global content nodes state - “Staging tree navigation”

Summary

When navigating the staging tree of a channel via the main tree navigation

content nodes are added to contentNodesMap Vuex state

https://github.com/learningequality/studio/blob/d6f06c273469ae8ad202774d40accc69817284ae/contentcuration/contentcuration/frontend/channelEdit/vuex/contentNode/index.js#L15

Example:

https://github.com/learningequality/studio/blob/a642f2ad00e9b8188a26892e225faec966dc3d4e/contentcuration/contentcuration/frontend/channelEdit/pages/StagingTreePage/index.vue#L387

The goal of this issue is to refactor the feature to not add/retrieve data to/from contentNodesMap and rather move towards using a more local state that will be cleared after a user stops using the feature.

Background

• We accumulate content nodes data in Vuex contentNode/state from various Studio features of the channelEdit app and there is no mechanism for clearing them which causes memory leaks. This issue is part of a larger group of issues (see https://github.com/learningequality/studio/issues/3363) that aim to refactor problematic features away from using Vuex global state towards private in-components state or state that’s shared between more components but is cleared at some point and optimized performance-wise in general.
• Ultimately, we want to get rid of globally stored content nodes data completely, however, this will be implemented incrementally, and therefore it’s fine to use mixed sources of data in the transition stage as long as all features continue working well from the user-point of view. Using composables is not required in all cases but is recommended as it has proven to be useful for state management across our products and it is flexible enough to allow us to keep using Vuex partially during the transition stage.

Acceptance criteria

• No content nodes are added/retrieved to/from contentNodesMap when navigating the staging tree of a channel via the main tree navigation (applies to all sub-components if there are any)
• The new implementation avoids the pitfalls of our current implementation that are described in the “Background” section and is optimized performance-wise overall

Notes

If you don't have a channel with the staging tree available yet for development and testing, you can follow "Reviewer guidance" in this PR https://github.com/learningequality/studio/pull/3004

Blocked by

• https://github.com/learningequality/studio/issues/3468

Blocking

• https://github.com/learningequality/studio/issues/3469

First review the Vuex content-node state in contentcuration/frontend/channelEdit/vuex/contentNode/index.js and the staging navigation usage in contentcuration/frontend/channelEdit/pages/StagingTreePage/index.vue. Check the blocker issue 3468 and the linked background issue before choosing an implementation. Done means staging-tree navigation and its sub-components no longer add or retrieve nodes through contentNodesMap while meeting the stated performance and cleanup goals.