Add the "@actions/exit" package

It is useful to have the exit logic separated into its own package

packages/exit/src/exit.ts

@@ -0,0 +1,43 @@
+/**
+ * The code to exit an action
+ */
+export enum ExitCode {
+  /**
+   * A code indicating that the action was successful
+   */
+  Success = 0,
+
+  /**
+   * A code indicating that the action was a failure
+   */
+  Failure = 1,
+
+  /**
+   * A code indicating that the action is complete, but neither succeeded nor failed
+   */
+  Neutral = 78
+}
+
+// TODO: These exit codes may not behave as expected on the new runtime, due to
+// complexities of async logging and sync exiting.
+
+/**
+ * Exit the action as a success.
+ */
+export function success() {
+  process.exit(ExitCode.Success)
+}
+
+/**
+ * Exit the action as a failure.
+ */
+export function failure() {
+  process.exit(ExitCode.Failure)
+}
+
+/**
+ * Exit the action neither a success or a failure
+ */
+export function neutral() {
+  process.exit(ExitCode.Neutral)
+}