Add VSCode Dev Container related configuration. (stellar#184)

.devcontainer/devcontainer.json

@@ -0,0 +1,14 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/ruby
+{
+	"name": "Ruby",
+	"image": "mcr.microsoft.com/devcontainers/ruby:1-3.2-bookworm",
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"Shopify.ruby-extensions-pack"
+			]
+		}
+	},
+	"postCreateCommand": "bundle install"
+}

.vscode/tasks.json

@@ -0,0 +1,17 @@
+{
+	// See https://go.microsoft.com/fwlink/?LinkId=733558
+	// for the documentation about the tasks.json format
+	"version": "2.0.0",
+	"tasks": [
+		{
+			"label": "Run tests",
+			"type": "shell",
+			"command": "if [[ -n $(git status -s) ]]; then echo \"Error: There are uncommitted files, please commit or discard the changes before executing this command.\"; exit 1; fi && rm -fr spec/output && bundle exec rspec && git add spec/output && git status && git diff --staged --exit-code -- spec/output || (echo \"Test outputs contain changes.\" && exit 1)",
+			"group": "test",
+			"presentation": {
+				"reveal": "always",
+				"panel": "new"
+			}
+		}
+	]
+}