dap: add debug adapter implementation

Adds a simple implementation of the debug adapter that supports the very
basics of a debug adapter.

It supports the launch request, the configuration done request, the
creation of threads, stopping, resuming, and disconnecting from server.

It does not support custom breakpoints, stack traces, or variable
inspection yet. These are planned to be added in the future.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

vendor/github.com/google/go-dap/doc.go

@@ -0,0 +1,20 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package dap contains data types and code for Debug Adapter Protocol (DAP) specification.
+// https://github.com/microsoft/vscode-debugadapter-node/blob/main/debugProtocol.json
+package dap
+
+//go:generate go run ./cmd/gentypes/gentypes.go -o schematypes.go -u cmd/gentypes/debugProtocol.json
+