Debugger UI does not display ErrorResponse from Variables Request

Does this issue occur when all extensions are disabled?: Yes

- VS Code Version: 1.137.0
- OS Version: Windows 11

Steps to Reproduce:

1. using Mock Debug from https://github.com/justarandomgeek/vscode-mock-debug/tree/error-response
2. Debug the test file to the `# Breakpoints` header
3. add a Watch expression `!bang` and observe it correctly displays the error response inline:

4. click the `lazyThrow` var and observe no UI response:

if the error `Message` object has `showUser` set then the error *will* be displayed as toast (lower right popups), but that seems undesirable in both cases, and if it is unset the Variables request produces no user feedback at all. Variables should display the error inline the same way Watch Evals do.