Fix getArgs support for node

[TerrorJack]

Closes #634.

This PR fixes getArgs for node. Say we compile test.hs and run node test.mjs extra flags, getArgs will properly return ["extra", "flags"].

The current implementation is just enough to support #640. Limitations compared to native getArgs:

• No support for setProgArgv.
• Total size of arguments must not exceed 1024 bytes.
• No handling for +RTS ... flags. See https://gitlab.haskell.org/ghc/ghc/-/blob/ghc-8.8/rts/RtsFlags.c#L612 for complete logic to handle them, which IMO is an unnecessary complexity to add for now.
• No support for getFullArgs.

[gkaracha]

I added some comment suggestions to document the more intricate parts of the PR.

Optionally, I think I'd also add a simple test:

import Asterius.Types
import Data.Coerce
import System.Environment

foreign import javascript "console.log($1)" js_print :: JSVal -> IO ()

js_print_string :: String -> IO ()
js_print_string s = js_print (coerce (toJSString s))

main :: IO ()
main = getArgs >>= print

(expected output: ["extra","flags"])

[TerrorJack]

@gkaracha Go ahead with the test then; remember to pull the weeds in the code snippet you pasted.

[gkaracha]

@gkaracha Go ahead with the test then; remember to pull the weeds in the code snippet you pasted.

1546735 should do it 🙂

[gkaracha]

The test indeed prints ["extra","flags"] as expected (see the very end of https://buildkite.com/tweag-1/asterius/builds/566#3daf7c98-89ea-4c20-8f8f-61f15b099545). This one is good to go.