Add support for pasting multi-line strings in Serial Monitor

[M65649]

Describe the problem

When pasting in a multi-line string in the serial monitor, line-feeds or carriage returns will be removed and replaced with space.

To reproduce

I used the following sketch to test:

void setup() {
  Serial.begin(9600);
}

void loop() {
  if (Serial.available()) {
    Serial.print((char)Serial.read());
  }
}

Pasting in the following:

1
2
3

Produces:

1 2 3 in the serial monitor. Can also verify via printing the hex values of the characters that the new lines are not included and replaced with space: 0x31 0x20 0x32 0x20 0x33. When printing the hex values and using e.g. PuTTY, one can see that the input correctly includes carriage returns.

Expected behavior

Expected behavior would be:

1
2
3

Arduino IDE version

2.1.2-nightly-20230807

Operating system

Windows

Operating system version

Window 10 22H2

Additional context

This feature is also not available when using the Arduino IDE 1.x Serial Monitor.

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the latest nightly build
• My report contains all necessary details

[kittaakos]

<input> cannot have line breaks. <textarea> looks more appropriate, but how to handle Enter. There are too many open questions.

[M65649]

What about Enter to send and Shift-Enter to insert a newline?