Clicking the "Validate completion" button from within a BigBlueButton activity results in an "invalidparameter: Invalid parameter value detected" error message.

Steps to reproduce:

1. Enable "Register live sessions" in BigBlueButton's experimental features
2. Create a BigBlueButton activity with activity completion enabled
3. Click on "Validate completion"

Expected result: A confirmation that the action was executed successfully

Actual result: Error message "Invalid parameter value detected"

This seems to be caused by a mismatch in how the bigbluebuttonbnid argument is passed from the event handler (https://github.com/moodle/moodle/blob/f7a8df253b0ff3fc8ad73135b645d4e9317b06cb/mod/bigbluebuttonbn/amd/src/rooms.js#L44) to the function generating the AJAX call (https://github.com/moodle/moodle/blob/f7a8df253b0ff3fc8ad73135b645d4e9317b06cb/mod/bigbluebuttonbn/amd/src/repository.js#L117).

The resulting request data is something like:

[{"index":0,"methodname":"mod_bigbluebuttonbn_completion_validate","args":4}] 

but it should be:

[{"index":0,"methodname":"mod_bigbluebuttonbn_completion_validate","args":{"bigbluebuttonbnid":"4"}}]