Fixes UART pin detach on Serial.end()

[SuGlider]

Description of Change

When Serial.end() is executed, the UART driver doesn't detach RX/TX/CTS/RTS pins.
As consequense, those pins pads connected using IOMUX by IDF layer will continue to send/receive data to/from the peripheral, causing the impression that Serial is still working.

This PR fixes it by adding a pin detach function used in Serial.end().

Tests scenarios

Tested using ESP32 and ESP32C3.

Necessary to use Arduino Serial Monitor for the default Board Serial port (Serial) and then some other UART<->USB converter board for reading the messages from pin 5 (new TX).

#define New_RX 4   // ESP32, S2, S3, C3
#define New_TX 5   // ESP32, S2, S3, C3

HardwareSerial NewSerial(0);

void setup() {
  Serial.begin(115200);
  delay(2000);

  Serial.println("\n\nStarting on Serial, default pins, and ending Serial");
  Serial.flush();
  Serial.end();
  delay(2000);

  NewSerial.begin(115200, SERIAL_8N1, New_RX, New_TX);
  delay(2000);
  
  NewSerial.println("\n\n...now printing on NewSerial, others pins .. " );
  NewSerial.println(" but the message appears also on Serial Monitor ... " );
  NewSerial.flush();
  Serial.println("\n\n printing on Serial");  // No output: OK serial is closed
  Serial.flush();
  NewSerial.println("\n\n and once more printing on NewSerial");
  NewSerial.flush();
}

void loop() {
  // put your main code here, to run repeatedly:
}

Related links

Fixes #7359

[fanfanlatulipe26]

Just need to add a "HardwareSerial NewSerial(0);" in the testcase

[SuGlider]

Just need to add a "HardwareSerial NewSerial(0);" in the testcase

Thanks! Added that line to the testcase!

[P-R-O-C-H-Y]

Good PR @SuGlider , tested on remaining chips S2/S3 and works great 👍