drivers: wifi: esp_at: handle commas in SSIDs during scan and status

SSIDs can contains commas (,) when receiving scan results (+CWLAP) or
status (+CWJAP) over AT command from ESP-AT chip. This is in conflict with
modem subsystem argument parsing, which separates arguments automatically
whenever comma is encountered.

Use a direct modem command parsing, so that commas within quoted strings
are taken into account to be part of that string, instead of being treated
as delimiter.

This solves `wifi scan` and `wifi status` Zephyr shell commands output, for
networks containing commas (like "My_2,4GHz_AP") as part of SSID.

Signed-off-by: Marcin Niestroj <m.niestroj@emb.dev>