Debugger: Add expression support to CliContext.

- Extend CliContext::Event to be able to store expression
  event results.
- Extend CliContext to watch for team expression events and
  handle them accordingly.
Debugger: Adapt CliDumpMemoryCommand to new expression interface.

- CliDumpMemoryCommand now requests asynchronous expression evaluation
  like the other users of expressions.
Debugger: Fix CID 1249932.

- Add missing member fields to initialization list.
Debugger: Fix CID 1249931.

- Add missing field to initializer list.