return the full path of 'Google Chrome' executable if found.
chrome_exec()chrome executable full path in a character vector of length 1.
Other executable full path:
excel_exec(),
firefox_exec(),
libreoffice_exec(),
node_exec(),
npm_exec(),
pip_exec(),
powerpoint_exec(),
python_exec(),
word_exec()
if(exec_available("chrome"))
message(chrome_exec())