[New] Parse `/` and `*` as a parameter in function definition

[Thirumalai-Shaktivel]

Example:

def _new(x, /):
    pass

Error:

$ lpython --show-ast --new-parser examples/expr2.py
syntax error: Token '/' is unexpected here
 --> examples/expr2.py:1:13
  |
1 | def _new(x, /):
  |             ^ 


Note: if any of the above error or warning messages are not clear or are lacking
context please report it to us (we consider that a bug that needs to be fixed).

Example 2:

def _new(*, x):
    pass

Error:

$ lpython --show-ast --new-parser examples/expr2.py
syntax error: Token ',' is unexpected here
 --> examples/expr2.py:4:11
  |
4 | def _new(*, x):
  |           ^ 


Note: if any of the above error or warning messages are not clear or are lacking
context please report it to us (we consider that a bug that needs to be fixed).