HardwareSerial Available For Write

[SuGlider]

Description of Change

When setting RX buffer, the setRxBufferSize() method would fail with values lower than 128 bytes.
Although it seems what IDF requests, it is not the best way to execute it, because the return value would be zero and the buffer size would be kept the same, by default 256. Now it returns the size it has been set, defining a minimum of 128+1 bytes, as required by IDF UART driver.

By other hand, for TX buffer, the setTxBufferSize() method also fails with less than 128 bytes, returning also 0.
With the change, it will return and set it to 128 (minimum), as requeired by IDF.
It also changes availableForWrite() in order to return a value that matches setTxBufferSize() when there is no data to be written, making it possible for applications to better compare and decide when to write to the UART.

Tests scenarios

Tested with ESP32 and ESP32-S3.

void setup() {
  size_t Ts = Serial.setTxBufferSize(100);
  size_t Rs = Serial.setRxBufferSize(100);
  Serial.begin(115200);
  delay(1000);
  
  Serial.printf("TX Buffer (%d) Size is %d\n", Ts, Serial.availableForWrite());
  Serial.printf("RX Buffer Size is %d\n", Rs);
}

void loop() {
  if (Serial.available()) {
    char c = Serial.read();
    Serial.write(c);
  }
}

Related links

Closes #9317

[github-actions]

	Warnings
⚠️	Some issues found for the commit messages in this PR: the commit message "feat(uart): setBufferSize ": body's lines must not be longer than 100 characters summary looks too short the commit message "feat: adjust availableForWrite": body's lines must not be longer than 100 characters the commit message "feat: sets TX buffer ": body's lines must not be longer than 100 characters summary looks too short Please fix these commit messages - here are some basic tips: follow Conventional Commits style correct format of commit message should be: <type/action>(<scope/component>): <summary>, for example fix(esp32): Fixed startup timeout issue allowed types are: change,ci,docs,feat,fix,refactor,remove,revert,test sufficiently descriptive message summary should be between 20 to 72 characters and start with upper case letter avoid Jira references in commit messages (unavailable/irrelevant for our customers) TIP: Install pre-commit hooks and run this check when committing (uses the Conventional Precommit Linter).
⚠️	The source branch "Serial_availableForWrite" incorrect format: contains uppercase letters. This can cause troubles on case-insensitive file systems (macOS). Please rename your branch.

	Messages
📖	You might consider squashing your 3 commits (simplifying branch history).

👋 Hello SuGlider, we appreciate your contribution to this project!

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