the simple version is that because `await` wasn't a keyword before, it can be a named function. So `await (x)` is ambiguous. Making the outer function `async f

the simple version is that because `await` wasn't a keyword before, it can be a named function. So `await (x)` is ambiguous. Making the outer function `async function () {...}` makes await a keyword inside that function, allowing them to move forward with that syntax in a non-breaking way as the parser now knows that there can't be a function named `await` inside any async functions.