chore: adds an action to assign reviewers from requested reviewers(#5642)

.github/workflows/scripts/assign_reviewers.js

@@ -0,0 +1,27 @@
+/**
+ * This script adds requested reviewers as assignees. If you remove a requested
+ * reviewer, it will not remove them as an assignee.
+ *
+ * See https://github.com/google/blockly/issues/5643 for more information on
+ * why this was added.
+ */
+exports.assign = function(github, context, core) {
+  try {
+    if (context.payload.pull_request === undefined) {
+      throw new Error("Can't get pull_request payload. Check a request reviewer event was triggered.");
+    }
+    const reviewers = context.payload.pull_request.requested_reviewers;
+    // Assignees takes in a list of logins rather than the reviewer object.
+    const reviewerNames = reviewers.map(reviewer => reviewer.login);
+    const {number:issue_number} = context.payload.pull_request;
+
+    github.rest.issues.addAssignees({
+      owner: context.repo.owner,
+      repo: context.repo.repo,
+      issue_number: issue_number,
+      assignees: reviewerNames
+    });
+  } catch (error) {
+    core.setFailed(error.message);
+  }
+}