📎 Implement json.parser.allowTrailingCommas

[Conaclos]

Description

As reported in #83, some config files support trailing comma.
json.parser.allowTrailingCommas: true enables trailing commas in json and jsonc files, making the following example valid:

{
  "prop1": [
    1,
    2,
  ],
  "prop2": 0,
}

Similar to json.parser.allowComments, json.parser.allowTrailingCommas: true should be enabled by default when parsing files such as tsconfig.json, VSCode config files, and others?

[nissy-dev]

I'm working