feat: add local devtainer for vsc

.devcontainer/Dockerfile

@@ -0,0 +1,3 @@
+ARG VER="gcc-9"
+
+FROM haydenkow/dcdev-kos-toolchain:${VER}

.devcontainer/devcontainer.json

@@ -0,0 +1,29 @@
+// For format details, see https://aka.ms/devcontainer.json.
+{
+	"name": "Dreamcast Dev",
+	"build": {
+		"dockerfile": "Dockerfile",
+		"args": { "VER": "gcc-9" }
+	},
+
+	// Set *default* container specific settings.json values on container create.
+	"settings": {},
+
+	// Add the IDs of extensions you want installed when the container is created.
+	// Note that some extensions may not work in Alpine Linux. See https://aka.ms/vscode-remote/linux.
+	"extensions": [
+		"ms-vscode.cpptools"
+	],
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	// "postCreateCommand": "uname -a",
+
+	// Replace when using a ptrace-based debugger like C++, Go, and Rust
+	// "runArgs": [ "--init", "--cap-add=SYS_PTRACE", "--security-opt", "seccomp=unconfined" ],
+
+	// Comment out connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+	 "remoteUser": "dev"
+}