Locates the first executable named program in the user's path, in the same way that execvp would locate it.
Returns an allocated string with the absolute path name, or null if the program is not
found in the path. If program is already an absolute path, returns a copy of program if program
exists and is executable, and null otherwise.
On Windows, if program does not have a file type suffix, tries with the suffixes .exe, .cmd, .bat and .com, and the suffixes
in the `PATHEXT` environment variable.
On Windows, it looks for the file in the same way as CreateProcess would. This means first in the directory where the
executing program was loaded from, then in the current directory, then in the Windows 32-bit system directory, then in the Windows
directory, and finally in the directories in the `PATH` environment variable. If the program is found, the return value contains the full
name including the type suffix.
| program |
a program name in the GLib file name encoding |
|
a newly-allocated string with the absolute path, or null |