Split the depsgraph allocation into a separate function
`BKE_scene_ensure_depsgraph()`. Parameters are only passed to those
functions that actually need them. This removes the the "if that boolean
is `false` this pointer is allowed to be `NULL`" logic and more cleanly
decouples code.
No functional changes.
This moves the `alembic`, `avi`, `collada`, and `usd` modules into a common
`io` directory.
This also cleans up some `#include "../../{somedir}/{somefile}.h"` by
adding `../../io/{somedir}` to `CMakeLists.txt` and then just using
`#include "{somefile}.h"`.
No functional changes.
