Flatten function expression parameters in hugged last argument

[thorn0]

Fixes #3376
This was done for arrow functions in #1305 ("Avoid breaking arguments for last arg expansion").
This PR enables the same for function expressions unless the function expression is the only argument.

Before:

function* mySagas() {
  yield effects.takeEvery(rexpress.actionTypes.REQUEST_START, function*({
    id
  }) {
    console.log(id);
    yield rexpress.actions(store).writeHead(id, 400);
    yield rexpress.actions(store).end(id, "pong");
    console.log("pong");
  });
}

After:

function* mySagas() {
  yield effects.takeEvery(
    rexpress.actionTypes.REQUEST_START,
    function* ({ id }) {
      console.log(id);
      yield rexpress.actions(store).writeHead(id, 400);
      yield rexpress.actions(store).end(id, "pong");
      console.log("pong");
    }
  );
}

Where did "unless the function expression is the only argument" come from? From code I found in the tests:

export class Thing12 implements OtherThing {
  do: (type: Type) => Provider<Prop> = memoize(function (
    type: ObjectType
  ): Provider<Opts> {
    return type;
  });
}

Apparently we want to keep it hugged.

• I’ve added tests to confirm my change works.
• (If changing the API or CLI) I’ve documented the changes I’ve made (in the docs/ directory)
• (If the change is user-facing) I’ve added my changes to changelog_unreleased/*/pr-XXXX.md file following changelog_unreleased/TEMPLATE.md.
• I’ve read the contributing guidelines.

✨Try the playground for this PR✨

[fisker]

@thorn0 sosukesuzuki/prettier-regression-testing#8 (comment)

Less changes than I thought it would be.

[fisker]

Suggested change

	path.getParentNode().arguments.length > 1
	getCallArguments(path.getParentNode()).length > 1

[thorn0]

We don't have such a function.

[thorn0]

But I see what you mean...

Prettier pr-9662
Playground link

--parser typescript

Input:

a=import(function(){})

Output:

TypeError: Cannot read property 'length' of undefined
    at https://deploy-preview-9662--prettier.netlify.app/lib/standalone.js:15:230593
    at Object.print (https://deploy-preview-9662--prettier.netlify.app/lib/standalone.js:15:270143)
    at Ri (https://deploy-preview-9662--prettier.netlify.app/lib/standalone.js:15:115017)
    at https://deploy-preview-9662--prettier.netlify.app/lib/standalone.js:15:114478
    at Object.printComments (https://deploy-preview-9662--prettier.netlify.app/lib/standalone.js:15:110760)
    at e (https://deploy-preview-9662--prettier.netlify.app/lib/standalone.js:15:114458)
    at https://deploy-preview-9662--prettier.netlify.app/lib/standalone.js:15:203119
    at Ti.call (https://deploy-preview-9662--prettier.netlify.app/lib/standalone.js:15:112552)
    at f (https://deploy-preview-9662--prettier.netlify.app/lib/standalone.js:15:203110)
    at Ti.call (https://deploy-preview-9662--prettier.netlify.app/lib/standalone.js:15:112552)

[fisker]

Yes we do... #9608