Migrate debugger panel and eval to use DAP instead of the VM Service

We would like to reduce the work required to support new language features by migrating part of Dart DevTools over to using [DAP.](https://microsoft.github.io/debug-adapter-protocol/)

DAP is the abstract protocol designed by Microsoft to be used between a debugging tool (e.g., VS Code, Dart DevTools) and a debugger (e.g., VM Service).

With Dart DevTools using the DAP interface to represent variables, we will only need to implement features in the Dart DAP package, instead of in both the Dart DAP package and in Dart DevTools.


Start by reading the DAP specification linked in the issue, then locate the debugger panel and eval implementation in Dart DevTools. Determine the current VM Service integration and the DAP interfaces needed; the work is done when those areas use DAP instead of the VM Service.

Written by the indexing model from the issue text.