[json] Format selection doesn't fix indentation

[jrieken]

• have the JSON snippet below
• select the 2nd line
• run "Format Selection"
• 🐛 the indentation isn't fixed

{
"foobar": true,
    "bazz": false
}

Originally posted by @misolori in #105800 (comment)

[aeschli]

Very unclear to me what the expect behavior of range format regarding the initial indentation.
Can we assume the content above is correctly formatted and indented?
Right now JSON builds on the original indent of the selected range.

TypeScript seems to look at the full file

{
{
var x; // selected line
}
}

=>

{
{
        var x; // selected line
}
}

[jrieken]

Yeah, I think the general approach is to format the whole document but to only generate text edits for nodes inside the selected range.