Release v1.12-tve2

This release incorporates a number of PRs that are stuck in the review queue on mainline.Specifically:

• micropython#5473 ESP32: support dynamic freq scaling and wifi power save
• micropython#5711 RFC #2: Mechanism for allowing dynamic native modules to call port-specific functionality.
• micropython#5819 extmod/modussl: improve exception error messages
• micropython#5825 extmod/modussl: fix socket and ussl read/recv/send/write errors for non-blocking sockets
• micropython#5834 esp32: add espidf_heap_info to esp32 module
• micropython#5840 moduasyncio: Add SSL support
• micropython#5850 esp32: consolidate check_esp_err functions
• micropython#5856 esp32: improve support for OTA updates

In addition, it fixes machine.RTC.memory on the ESP32 and provides access to ESP-IDF functions needed to implement SNTP.

The attached binaries are images for the ESP32 GENERIC_OTA "board". The firmware.bin is for flashing over USB and the application.bin is for OTA updates (over MQTT). The USB image can be flashed as follows:

esptool.py --chip esp32 --port /dev/ttyUSB0 --baud 460800 write_flash -z --flash_mode dio --flash_freq 80m 0x1
000 mp-esp32-generic-ota-v1.12-tve2-0-g251c8f5a3-firmware.bin