Address 2637: Relax promise-function-async for short arrow functions

[rrogowski]

PR checklist

• Addresses an existing issue: fixes Relax promise-function-async for short arrow functions #2637
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

Single statement lamda functions that delegate to another promise-returning function are allowed.

Configuration

{
  "rules": {
    "promise-function-async": true
  }
}

Before

public async asyncPromiseMethodB() {
    return new Promise<void>();
}

public delegatingMethod = () => this.asyncPromiseMethodB(1);
                          ~~~~~ [functions that return promises must be async]

After

public async asyncPromiseMethodB() {
    return new Promise<void>();
}

public delegatingMethod = () => this.asyncPromiseMethodB(1);
                          // No lint error

CHANGELOG.md entry:

[enhancement] promise-function-async now allows single statement lamda functions that delegate to another promise-returning function

[JoshuaKGoldberg]

LGTM, thanks @rrogowski! 🙌