Implement fixall support in VSCode extension

It would be great for a consistent developer experience in VSCode to support the `fixall` statement like in `eslint`. The VSCode settings could look like this:

```json
"editor.codeActionsOnSave": {
"source.fixAll": true,
}
```

or

```json
"editor.codeActionsOnSave": {
"source.fixAll.bicep": true
}
```

Start by locating the VSCode extension's existing code-action handling and review how ESLint exposes the `source.fixAll` and `source.fixAll.bicep` settings shown in the issue. Confirm the expected behavior for both settings and verify that saving a file invokes the available fixes consistently.

Written by the indexing model from the issue text.