Migrate Stream search internals from char to uint8_t

[asumo-1xts]

(I'm still new to contributing to OSS, so please let me know if there's anything I need to correct!)

Overview

This PR is regarding issue #119.

In the current code, Stream::find() cannot find values above 0x7f because it treats the target string as char.
This PR fixes the issue by changing the target string type from char to uint8_t.

Verification on an actual device

I confirmed with an Arduino UNO R3 clone that the sketch below does not blink the built-in LED with the current code, but it does blink with the fixed code.

Note

It performs serial communication from its own TX to its own RX.
Please make sure to connect the TX and RX pins after uploading the sketch.

Note

To build the sketch correctly, you may need to rewrite the header-include in Stream.cpp:
Common.h -> Arduino.h

// It performs serial communication from its own TX to its own RX.
// Please make sure to connect the TX and RX pins after uploading the sketch.

#include <Arduino.h>

const uint8_t TEST_NUMBER = 0x80; // above 0x7f

void setup() {
  Serial.begin(115200);
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  Serial.write(TEST_NUMBER);
  delay(1000);

  if (Serial.available()) {
    if (Serial.find(TEST_NUMBER)) {
      digitalWrite(LED_BUILTIN, HIGH);
      delay(500);
      digitalWrite(LED_BUILTIN, LOW);
      delay(500);
    }
  }
}

[CLAassistant]

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