Support `import` aliases

[rebcabin]

repro: https://github.com/rebcabin/lpython/tree/brian-lasr/lasr/LP-pycharm/Issue2025

offending code lasr_parser.py:

import lasr_lexer as ll
# from lasr_lexer import LasrLexer  # workaround

from lpython import i32, dataclass

@dataclass
class Node:
    lexer : ll.LasrLexer = ll.LasrLexer()

run (shows CPython passing:

(lp) ┌─(~/CLionProjects/lpython/lasr/LP-pycharm/Issue2025)───────────────────────────────────────────────────────────────────────────────────────────────(brian@Golf37:s012)─┐
└─(10:52:57 on brian-lasr ✭)──> ~/CLionProjects/lpython/src/bin/lpython -I. lasr_parser.py                                                                ──(Sun,Jun25)─┘
semantic error: 'll' is not defined in the scope
  --> lasr_parser.py:10:13
   |
10 |     lexer : ll.LasrLexer = ll.LasrLexer()
   |             ^^^^^^^^^^^^ 


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 must be fixed).
(lp) ┌─(~/CLionProjects/lpython/lasr/LP-pycharm/Issue2025)───────────────────────────────────────────────────────────────────────────────────────────────(brian@Golf37:s012)─┐
└─(10:55:13 on brian-lasr ✭)──> PYTHONPATH='../../../src/runtime/lpython' python lasr_parser.py                                                       2 ↵ ──(Sun,Jun25)─┘
(lp) ┌─(~/CLionProjects/lpython/lasr/LP-pycharm/Issue2025)───────────────────────────────────────────────────────────────────────────────────────────────(brian@Golf37:s012)─┐
└─(10:56:00 on brian-lasr ✭)──> 

workaround (both LP and CP pass):

# import lasr_lexer as ll
from lasr_lexer import LasrLexer  # workaround

from lpython import i32, dataclass

@dataclass
class Node:
    lexer : LasrLexer = LasrLexer()  ############ ATTENTION ############