youtube.lua: add "n" descrambling split compound transformations

A new variant of compound transformation has the Base64 alphabet
generation and the compounding itself as two separate data array
elements, contrary to what was observed so far. Add support for those.

Fixes #26285

(cherry picked from commit 7f6614cb)
Signed-off-by: Hugo Beauzée-Luyssen <hugo@beauzee.fr>