Uses discourse/onebox@ff9ec90
Adds a hidden site setting called disable_onebox_media_download_controls which will add controlslist="nodownload" to video and audio oneboxes, and also to the local video and audio oneboxes within Discourse.
Zeitwerk simplifies working with dependencies in dev and makes it easier reloading class chains.
We no longer need to use Rails "require_dependency" anywhere and instead can just use standard
Ruby patterns to require files.
This is a far reaching change and we expect some followups here.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
