clang-format: [JS] tests for async wrapping.

[mprobst]

Summary

Adds tests to ensure that async method() ... does not wrap between async and
the method name, which would cause automatic semicolon insertion.

clang/unittests/Format/FormatTestJS.cpp

verifyFormat("async function f() {\n"
                "}\n",
                "  async   function f() {\n"
                "   return 1;\n"
                "}\n"
                "\n"
                "   function a() {\n"
                "  return   1;\n"
                "}  \n");
+  // clang-format must not insert breaks between async and function, otherwise
+  // automatic semicolon insertion may trigger (in particular in a class body).
+  verifyFormat("async function\n"
+               "hello(\n"
+               "    myparamnameiswaytooloooong) {\n"
+               "}",
+               "async function hello(myparamnameiswaytooloooong) {}",
+               getGoogleJSStyleWithColumns(10));
+  verifyFormat("class C {\n"
+               "  async hello(\n"
+               "      myparamnameiswaytooloooong) {\n"
+               "  }\n"
+               "}",
+               "class C {\n"
+               "  async hello(myparamnameiswaytooloooong) {} }",
+               getGoogleJSStyleWithColumns(10));
   verifyFormat("async function* f() {\n"
                "  yield fetch(x);\n"
                "}");
   verifyFormat("export async function f() {\n"
                "  return fetch(x);\n"
                "}");
   verifyFormat("let x = async () => f();");
   verifyFormat("let x = async function() {\n"