[DAP] Provide a way to send back a response after a hot response request

[elliette]

The base DartDebugAdapter restartRequest has a sendResponse callback that doesn't accept any parameters:

sdk/pkg/dds/lib/src/dap/adapters/dart.dart

Line 1335 in 1405695

void Function() sendResponse,

It would be nice if implementations of the debug adapter could send back a response after doing a hot-restart. This requires defining a response type that the sendResponse callback would take as a parameter.