Print run-js return value

[Aylur]

if a single javascript statement (meaning it doesn't have a semicolon) is passed to --run-js it will print it to stdout
if the passed argument has a semicolon, whatever this passed function returns will be printed to stdout

# prints current date
ags --run-js "new Date()"
ags --run-js "const date = new Date(); return date;"

# prints undefined
ags --run-js "new Date();"

this PR also introduces the --run-promise flag which allows running async functions and print with resolve or reject

ags --run-promise "ags.Utils.timeout(1000, () => resolve('a second later'))"