vscode edit snippet for existing extension code example

Example: vscode user snippets

"For Loop": {
    "prefix": "for",
    "body": [
        "for (var ${index} = 0; ${index} < ${array}.length; ${index}++) {",
        "\tvar ${element} = ${array}[${index}];",
        "\t$0",
        "}"
    ],
    "description": "For Loop"
},