py/runtime: Allow multiple *args in a function call.

This is a partial implementation of PEP 448 to allow unpacking multiple
star args in a function or method call.

This is implemented by changing the emitted bytecodes so that both
positional args and star args are stored as positional args.  A bitmap is
added to indicate if an argument at a given position is a positional
argument or a star arg.

In the generated code, this new bitmap takes the place of the old star arg.
It is stored as a small int, so this means only the first N arguments can
be star args where N is the number of bits in a small int.

The runtime is modified to interpret this new bytecode format while still
trying to perform as few memory reallocations as possible.

Signed-off-by: David Lechner <david@pybricks.com>

tests/basics/python34.py.exp

@@ -1,13 +1,8 @@
-None
-['a', 'b']
-('a', 'b') {'kw_arg': None}
 2
 1
 SyntaxError
 SyntaxError
 SyntaxError
-SyntaxError
-SyntaxError
 3.4
 3 4
 IndexError('foo',)