Required fields aren't being validated

[rzhao271]

Ref #129499

Required properties behave strangely with object settings in the settings editor. Let's say A is required and B isn't. Then consider the following setting value:

"settingName": {
 "B": "v2"
}

and assume A has a default value of v1.

The JSON editor displays a warning saying A is missing. However, the GUI editor displays A with the value v1, still, with no warning. However, if A isn't given a default value, but is still required, the GUI editor doesn't display A, but there's still no warning on the GUI editor side.

[rzhao271]

Code pointer: https://github.com/microsoft/vscode/blob/main/src/vs/workbench/contrib/preferences/browser/settingsTree.ts#L136

The default value is being placed in here, which ends up rendering it, even though the user didn't specify it in the settings json file.

[rzhao271]

It turns out the above code is necessary, otherwise default values would have to be saved into the settings JSON file for every setting.

The only time a default value needs to be saved into the settings JSON file would be if:

1. The user manually defined a setting in the settings JSON file AND
2. The default value corresponds to a required property

I also confirmed that many extensions use object settings with required keys.