Fix no-this-in-sfc rule behavior for arrow functions inside a class field

[sergei-startsev]

Fixed #1967. Adjusted component detection in getParentStatelessComponent for arrow functions inside a class field, e.g.:

class Foo {
  bar() { 
    () => {
      this.something();
      return null;
    };
  }
}

See details in #1972.

[ljharb]

Is this meant to be checking the same thing twice?

[sergei-startsev]

good catch, it should be FunctionExpression and FunctionDeclaration

[sergei-startsev]

Fixed typo and added one more more test.

[ljharb]

I don't see any tests of function declarations tho (arrows are only ever expressions)

[sergei-startsev]

@ljharb A parent scope of arrow function can have FunctionDeclaration type. The check is required to detect parent function scope for arrow expressions properly. I've added a test to illustrate it.