Added a new cmd_array() method to the ExternalProgram object that returns an array containing the command(s) for the program. This is particularly useful in cases like pyInstaller where the Python command is meson.exe runpython, and the full path should not be used but rather the command array.
The method returns a list of strings representing the complete command needed to execute the external program, which may differ from just the full path returned by full_path() in cases where wrapper commands or interpreters are involved.