Simplify exec_byte_code arguments

Simplify exec_byte_code arguments

Pass the function object and encoded arity, not the other components.
This speeds up several call paths and is necessary for improvements to
come.

* src/bytecode.c (Fbyte_code): Make a new byte code object for
execution.  This is slower but performance isn't critical here.
(exec_byte_code): Retrieve components from the passed function.
* src/eval.c (fetch_and_exec_byte_code):
* src/lisp.h (exec_byte_code): Update signature.