[WiFi] Cleanup code, split ESP32/ESP8266 specific

[TD-er]

Finally going to clean up the WiFi code and restructure it.
Hopefully this will also show where the long lasting WiFi reconnect issues may be...

Fixes: #3870

ToDo:

• Fix WiFi Captive portal
• Load CSS on /setup page when connected via softAP
• Keep softAP active as long as some client is connected (WiFi.softAPgetStationNum() does not work as expected on ESP8266)
• Allow to keep AP_only mode active
• Perform WiFi scan on /setup page when "Rescan" button is pressed
• Call WiFi_AP_Candidates.force_reload() when saving security settings
• Make clear state whether we're still in "setup" mode
• Re-open AP mode if in "setup" mode and login failed
• Cleanup old code
• Test hidden SSID functionality
• Test static IP functionality
• Fix JSON on Devices tab when there are no tasks configured ("Sensors":[] missing)
• Console not working when HWCDC is enabled and nothing connected to that port
• RMII Ethernet sometimes needs a power cycle, when MAC address reads 00:00:00:00:00:00
• SPI Ethernet seems to get the same MAC address as WiFi AP (at least with W5500 + ESP32S3)
• SPI Ethernet doesn't seem to get Global IPv6 address
• ESPEasy p2p still seems to try process UDP packet after interface is down, causing crash
• ESP32-S3 sometimes doesn't find AP on first scan, then takes minutes to retry
• Need to convert any existing Ethernet configuration into a newly added Ethernet device on Network tab
• WiFi config added via setup page should try to store in empty slot first
• Document how to flash ESP-Hosted-MCU for ESP32-P4 when firmware 0.0.6 is loaded on external ESP32-C6/C5 Espressif web flash page
• Add command to toggle route priority and/or default flag via rules.
• Remove mixed pin labels for RMII/SPI Ethernet pins (e.g. "Ethernet MDC/CS pin" )
• Add command to setup Ethernet config in a single copy/paste via command line
• Keep track of previous attempts on ESP32-P4 to try detect whether ESP-Hosted-MCU is present, since ESP may crash when no firmware is present, SDIO pins are incorrect or firmware is too old (default factory firmware of first P4 board had either no fw or version 0.0.6)
• Keep WiFi off at initial boot unless explicitly started. For example for ESP32-P4 boards or some ESP32-classic boards with no WiFi present like some M5Stack boards.
• Add info from here in the docs
• Make IPv6 optional per interface

[TD-er]

Notes/bookmarks:

AP API: https://github.com/espressif/arduino-esp32/blob/master/libraries/WiFi/src/WiFiAP.h#L44-L57
STA API: https://github.com/espressif/arduino-esp32/blob/master/libraries/WiFi/src/WiFiSTA.h#L49-L83
ETH API: https://github.com/espressif/arduino-esp32/blob/master/libraries/Ethernet/src/ETH.h#L125-L163
PPP API: https://github.com/espressif/arduino-esp32/blob/master/libraries/PPP/src/PPP.h#L26-L80
Common for every interface: https://github.com/espressif/arduino-esp32/blob/master/libraries/Network/src/NetworkInterface.h#L39-L76

Manager api:
Main: https://github.com/espressif/arduino-esp32/blob/master/libraries/Network/src/NetworkManager.h#L17-L31
Events: https://github.com/espressif/arduino-esp32/blob/master/libraries/Network/src/NetworkEvents.h#L143-L219

Network.setDefaultInterface(NetworkInterface &ifc); takes as argument STA, ETH or PPP
This allows to set which of those is used for Internet.

[tonhuisman]

Shouldn't that be NETWORK_MAX ?

[TD-er]

Yes it should...