embedded stdlib

This PR embeds the stdlib into the dagger binary itself for convenience.
Long term we will want to source the stdlib directly from git.

- Updated go to 1.16 to use the new built-in embedding functionality
- The `stdlib` go package now contains an embed of the stdlib

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

stdlib/yarn/yarn.cue

@@ -0,0 +1,64 @@
+package yarn
+
+import (
+	"dagger.cloud/dagger"
+)
+
+// Yarn Script
+#Script: {
+	// Source code of the javascript application
+	source: dagger.#Dir
+
+	// Run this yarn script
+	run: string | *"build"
+
+	// Read build output from this directory
+	// (path must be relative to working directory).
+	buildDirectory: string | *"build"
+
+	// Set these environment variables during the build
+	env?: [string]: string
+
+	#dagger: compute: [
+		dagger.#FetchContainer & {
+			ref: "alpine@sha256:08d6ca16c60fe7490c03d10dc339d9fd8ea67c6466dea8d558526b1330a85930"
+		},
+		dagger.#Exec & {
+			args: ["apk", "add", "-U", "--no-cache", "bash=5.1.0-r0"]
+		},
+		dagger.#Exec & {
+			args: ["apk", "add", "-U", "--no-cache", "yarn=1.22.10-r0"]
+		},
+		dagger.#Exec & {
+			args: [
+				"/bin/bash",
+				"--noprofile",
+				"--norc",
+				"-eo",
+				"pipefail",
+				"-c",
+				"""
+					yarn install --production false
+					yarn run "$YARN_BUILD_SCRIPT"
+					mv "$YARN_BUILD_DIRECTORY" /build
+					""",
+			]
+			if env != _|_ {
+				"env": env
+			}
+			"env": {
+				YARN_BUILD_SCRIPT:    run
+				YARN_CACHE_FOLDER:    "/cache/yarn"
+				YARN_BUILD_DIRECTORY: buildDirectory
+			}
+			dir: "/src"
+			mount: {
+				"/src": from: source
+				"/cache/yarn": "cache"
+			}
+		},
+		dagger.#Subdir & {
+			dir: "/build"
+		},
+	]
+}