Rename all proposal plugins to -proposal- from -transform- (#6570)

packages/babel-plugin-proposal-optional-catch-binding/src/index.js

@@ -0,0 +1,17 @@
+import syntaxOptionalCatchBinding from "@babel/plugin-syntax-optional-catch-binding";
+
+export default function() {
+  return {
+    inherits: syntaxOptionalCatchBinding,
+
+    visitor: {
+      CatchClause(path) {
+        if (!path.node.param) {
+          const uid = path.scope.generateUidIdentifier("unused");
+          const paramPath = path.get("param");
+          paramPath.replaceWith(uid);
+        }
+      },
+    },
+  };
+}