Add DAP configuration for Dart and Flutter

This has some issues still, but I want to let people know about it at least.

Currently running a test program results in the following output:

{
    "command": [
        "dart",
        "debug_adapter"
    ],
    "request": {
        "args": [
        ],
        "command": "launch",
        "mode": "debug",
        "program": "/home/bart/Documents/Git/personal/test_dap/bin/test_dap.dart"
    }
}


server capabilities:
* conditional breakpoints: supported
* function breakpoints: unsupported
* hit conditional breakpoints: unsupported
* log points: supported
* modules request: unsupported
* goto targets request: unsupported
* terminate request: supported
* terminate debuggee: unsupported

*** waiting for user actions ***
--> (running)
Connecting to VM Service at ws://127.0.0.1:44995/KVShJcJaOWA=/ws

--> (started) thread 1Hello world: 42!
This is executed via the DAP!

--> stopped (pause). Active thread: 1.
--> (exited) thread 1
error on response: No thread with threadId 1

Exited.
--> program terminated
requesting disconnection
requesting shutdown
*** connection with server closed ***
DAP backend: Process crashed
DAP backend: process exited with code 15

That is with the following code:

import 'package:test_dap/test_dap.dart' as test_dap;

void main(List<String> arguments) {
  print('Hello world: ${test_dap.calculate()}!');

  print("This is executed via the DAP!");
}

The print's indicate the program ran successful, but when it's closed the DAP seems to be crashing. I don't know if that is a problem in the Dart DAP of in Kate.