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

packages/babel-plugin-proposal-async-generator-functions/test/fixtures/async-generators/expression/actual.js

@@ -0,0 +1,6 @@
+(async function* agf() {
+  this;
+  await 1;
+  yield 2;
+  return 3;
+});

packages/babel-plugin-proposal-async-generator-functions/test/fixtures/async-generators/expression/expected.js

@@ -0,0 +1,14 @@
+(() => {
+  var _ref = babelHelpers.wrapAsyncGenerator(function* () {
+    this;
+    yield babelHelpers.awaitAsyncGenerator(1);
+    yield 2;
+    return 3;
+  });
+
+  function agf() {
+    return _ref.apply(this, arguments);
+  }
+
+  return agf;
+})();