It seems Theia can't show debug evaluate errors, because of incorrect DAP error handling

[EvilBeaver]

Bug Description:

When trying to evaluate expression in debugger, debug adapter can return success: false and error description. This is common thing that expressions can be misprinted and contain errors.

But, it seems Theia doesn't honor success flag of response https://github.com/eclipse-theia/theia/blob/master/packages/debug/src/browser/console/debug-console-items.tsx#L318 and shows error UI only in case of exception, which is not thrown in case of evaluation error.

Steps to Reproduce:

1. Start debug session of some language and stop it on breakpoint
2. Print something wrong and incorrect in "watch" widget
3. Error is not shown, instead we see "not available" message

Expected, that real error is shown in an "error" manner, with Severity.Error

Reason: Theia tries to show a successful evaluation resultm which is "not available" because debug adapter returned error, not a result.

Additional Information

• Operating System: any
• Theia Version: Version 1.31.1 (Beta)