fix(palm): receive XBlock visibility from the Learning MFE

[Agrendalath]

Currently, the LMS retrieves the viewport information with getBoundingClientRect. However, it doesn't work correctly when the XBlocks are rendered in an iframe because the iframe is automatically resized to its full height.

This solves the described problem by sending the visibility status from the Learning MFE to the LMS.

Testing instructions:

1. (Optional) Set COMPLETION_BY_VIEWING_DELAY_MS = 1000 in lms/envs/private.py for easier testing. The default value is 5000.
2. (Optional) Change publish_completion to publish_completions in lms/static/completion/js/CompletionOnViewService.js for easier testing. Otherwise, you will need to create a new XBlock for the next check or manually remove the BlockCompletion object from the DB to get the API call re-triggered the next time you view it.
3. Check out the current PR and fix(palm): send XBlock visibility status to the LMS frontend-app-learning#16.
4. Create an HTML block with a single line. Check that the publish_completion request is called in both the Learning MFE and the Preview (to check for regressions).
5. Create two HTML blocks with enough lines to exceed your viewport. Check that the publish_completion request is called when you scroll down to the bottom of each of these blocks (in the Learning MFE and Preview).

Private-ref: BB-8826

[xitij2000]

👍

• I tested this: tested on palm tutor devstack
• I read through the code

[Agrendalath]

Palm-specific tests are passing. Merging.