Fixing argument parsing on Windows

[edublancas]

When working on #424, I realized we have an error when parsing the arguments passed to the SQL query (e.g., %sql SELECT * FROM table --persist - note that we have to parse the query and the --persist argument).

This is because we're relying on parse_argstring from IPython, which behaves differently on Windows and will delete quotes that are necessary for a SQL query to run, here's how to reproduce it.

from IPython.core.magic_arguments import parse_argstring
from sql.magic import SqlMagic
from IPython import get_ipython

%load_ext sql

Console output (1/1):

The sql extension is already loaded. To reload it, use:
  %reload_ext sql

ip = get_ipython()
magic = ip.find_magic("sql")

We're using this function internally to parse arguments, note that the query has "table spaces" in double quote:

parse_argstring(magic, 'create table "table spaces" (n INT)').line

On Windows, the double quotes disappear (this doesn't happen on mac or linux):

Console output (1/1):

['create', 'table', 'table spaces', '(n', 'INT)']

This happens because on linux/mac, the _process_common function is used:

from IPython.utils._process_common import arg_split
arg_split('create table "table spaces" (n INT)')

Console output (1/1):

['create', 'table', '"table spaces"', '(n', 'INT)']

But on Windows, the _process_win32 is used:

from IPython.utils._process_win32 import arg_split
arg_split('create table "table spaces" (n INT)')

Console output (1/1):

['create', 'table', 'table spaces', '(n', 'INT)']

---

I think we can fix this by changing our magic_args function in parse.py:

import shlex

def magic_args(magic_execute, line):
    line = without_sql_comment(parser=magic_execute.parser, line=line)
    return magic_execute.parser.parse_args(shlex.split(line, posix=False))

But I'm unsure if there would be any side effects.

---

Some IPython links:

https://github.com/ipython/ipython/blob/a3d5a06d9948260a6b08c622e86248f48afd66c3/IPython/utils/_process_win32.py#L29

https://github.com/ipython/ipython/blob/a3d5a06d9948260a6b08c622e86248f48afd66c3/IPython/utils/_process_common.py#L25

https://github.com/ipython/ipython/blob/a3d5a06d9948260a6b08c622e86248f48afd66c3/IPython/core/magic_arguments.py#L164

[bbeat2782]

Acceptance Criteria

1. Using either double or single quote to enclose a space when using %sql, %sqlplot, or %sqlcmd should work. (e.g %sql create table "table spaces" (n INT), %sqlplot bar --table 'file with spaces.csv' --column x, or %sqlcmd columns -t 'table with spaces' should work)
2. Add test functions

[edublancas]

go ahead! the easiest way to get started is to try the solution I propose at the end, and then see if all tests pass and if there are any edge cases