Add strong indication when development build completes

[danfinlay]

Ideally a big green log, or maybe even a sound.

Since the snaps-beta is live, we have more devs than ever running development builds of MetaMask, and not knowing when the build is complete is a recurring point of confusion.

[crazyrabbitLTC]

Yes, this would be super helpful. :-) I'm still not sure when it's done done. ;-)

[rekmarks]

It would also be nice to have a progress bar!

[dodonpaa]

when I ran "yarn start", the script was frozen at "scripts:core:dev:standardEntryPoints: Bundle end: "primary". I had to press Ctrl+c to exit the script. I'm not sure if the build was complete. Does anyone know if this is expected behavior or a bug in the build script?