vs.commands.executeCommand("vscode.executeCodeActionProvider") loses keepWhitespace field from SnippetTextEdits

In my extension I created a codeActionsProvider that returns a`WorkspaceEdit` that contains a `SnippetTextEdit` with `keepWorkspace=true`:

```ts
vs.languages.registerCodeActionsProvider({ scheme: "file" }, {
provideCodeActions(_document, _range, _context, _token) {
const snippet = new vs.SnippetTextEdit(
new vs.Range(
new vs.Position(0, 0),
new vs.Position(0, 0),
),
new vs.SnippetString("${1:widget}"),
);
snippet.keepWhitespace = true;
const edit = new vs.WorkspaceEdit();
edit.set(vs.Uri.parse("foo://foo"), [[snippet, undefined]]);

const action = new vs.CodeAction("My Action");
action.edit = edit;
return [
action
];
},
});
```

If, in a test, I call `vs.commands.executeCommand("vscode.executeCodeActionProvider")` like this:

```ts
const actions = await vs.commands.executeCommand("vscode.executeCodeActionProvider", flutterEmptyFile, new vs.Range(new vs.Position(0, 0), new vs.Position(0, 0)));
```

The `keepWhitespace` flag gets lost, and if I then use `vs.workspace.applyEdit()` on it, the whitespace is not kept (instead, VS Code changes it, believing the returned action didn't already have the correct whitespace).

Here's what inspecting the edit looks like in the extension side:

And here's what it looks like on the test side: