Add Karma js tests in extracted video xblock

[salman2013]

Description

Add Karma JS tests in extracted video xblock.

[salman2013]

PR for this ticket: openedx/xblocks-core#92

[salman2013]

PR for this ticket: openedx/xblocks-core#92

[farhan]

Ticket implementation has been completed in the above shared PR.
It will be merged once following video xblock extraction will be merged.
openedx/openedx-platform#36282