Better detection of required serial port during upload.

[cmaglie]

Previously we checked the upload recipe for the variable {serial.port} to determine if the upload requires a serial port, but this is not sufficient because we must check also for the variable {serial.port.file}.
No breaking changes.

Current output:

$ arduino-cli upload --dry-run -v -b arduino:samd:adafruit_circuitplayground_m0
Skipping 1200-bps touch reset: no serial port selected!
Waiting for upload port...
No upload port found, using  as fallback
"/home/megabug/.arduino15/packages/arduino/tools/bossac/1.7.0-arduino3/bossac" -i -d --port={serial.port.file} -U true -i -e -w -v "/tmp/arduino-sketch-61DECCCDDA68480BC07770DEB6E56DDB/Bare.ino.bin" -R

As we can see the bossac tool is launched anyway with the unexpanded {serial.port.file} variable.

New behavior:

$ arduino-cli upload --dry-run -v -b arduino:samd:adafruit_circuitplayground_m0
Skipping 1200-bps touch reset: no serial port selected!
Waiting for upload port...
No upload port found, using  as fallback
Error during Upload: uploading error: no upload port provided

The message No upload port found, using as fallback can be still improved, but at least we have a clear indication that the error is caused by no upload port provided.