Fix system headers, review and simplify

[mikee47]

This PR removes some long-deprecated code and build logic from the framework,
and fixes some low-level (system) header file inconsistencies between architectures.

user_config.h

This header was removed from samples in #1695.
It's a hangover from the Espressif SDK applications and doesn't fit very well into the framework structure.

The file has been removed from all framework code but one copy left with a deprecation warning.
Note added to upgrade docs.

System header files

Each architecture has a set of system header files, located here:

• Arch/Esp8266/Components/esp8266
• Arch/Esp32/Components/esp32
• Arch/Host/Components/esp_hal
• Arch/Rp2040/Components/rp2040

In particular the ESP8266 SDK headers are problematic so have been moved into the esp8266 Component:

• Remove sntp.h as can just use lwip/sntp.h
• Apply coding style, fix type definitions for consistency
• Integrate 'missing' SDK definitions - these are no longer scattered around on an ad-hoc basis
• Split out user_interface.h into esp_system.h and esp_wifi.h
• LWIP_OPEN_SRC is always true so can remove SDK version of ip_addr.h
• Move BIT, TRUE, FALSE, LOCAL macros into c_types.h

For other architectures:

• Move os_random and os_get_random into esp_system (get rid of esp_libc)
• Remove system_set_os_print and ets_install_putc1 (not used)

Remove pre-SDK 3 support

There was an issue with small flash sizes but this now seems to be resolved.
Tested with Basic_Blink sample and 256K, 512K flash size, no problem.
Now using only libraries from the SDK: all header/linker files are in framework.

Simplifies build system and code. SDK_BASE definition is no longer publicised.

SDK submodule renamed from ESP8266_NONOS_SDK to sdk.

lwip

• Use single lwip_includes.h file, relocated to Network Component, rather than one-per-arch
• Fix esp_open_lwip
• Fix lwip2, but as it's forked can use that instead of patching

Other simplifications

• esp8266 esp_cplusplus.h header not necessary, single function used only by startup code
• Remove new-pwm submodule, replace with patched source instead
• Provide better esp32 system_get_time implementation
• Remove deprecated headers (including SmingCore/SmingCore.h)
• Move SERIAL_BAUD_RATE, ESP8266_EX and ESP32_EX definitions into makefiles

Build system

• Fix issue with missing Component -clean targets.
  e.g. make lwip2-clean will always fail because ENABLE_CUSTOM_LWIP option never gets set, so lwip2-clean target never gets created

• Fix component-samples build target, should honour COMPONENT_SOC setting

• Fix component-samples-clean build target, broken

Integration tests

Add component-samples to esp32 build, requires only a few simple library fixes to build all variants.