Cleanup c2rust output in cdef_apply.rs

[randomPoison]

• Cleanup helper functions to take safe arguments where possible (may take raw pointers as arguments currently).
• Cleanup state machine control flow (current_block and friends) in rav1d_cdef_brow.
• General cleanup of c2rust generated code in functions.
• Restore comments from original C.

[randomPoison]

Fixed by #738 and #733.