[json] add commas automatically

Test case

Expected behavior

• After typing age <kbd>TAB</kbd>, the comma should be added to the end of the previous line.
• After typing " for the next object property, the comma should be added to the end of the previous line.

Actual behavior

The autocomplete does not produce valid text.

Discussion

In general, the autocomplete should strive to produce output that is maximally valid in whatever language grammar it is using.

[peteruithoven]

It’s most annoying when you add a { and VS Code auto adds the } at the end.

I get in this situation all the time:

const value = {
  a: "a",
  b: {
    
  }
  c: "c"
}

It’s very common in Vue’s option syntax for example.

[fulldecent]

Got it @zardoy, I have updated the expected behavior above and added another behavior that doesn’t require auto complete