Change the getError and hasError signature to have more flexibility #19734

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[X ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior

Currently the methods AbstractControl#getError and AbstractControl#hasError accept a 2nd. parameter that let you specify the path of the control. Ex:

formGroup.hasError('errorCode', ANYPATH);

However, both of these methods have the following signature:

getError(errorCode: string, path?: string[]): any

 hasError(errorCode: string, path?: string[]): boolean

... and behind the scenes these methods just call the AbstractControl#get method, which one accepts a string or an array of number | string.

Doesn't it make sense to change the signatures to the same of get method?

getError(errorCode: string, path?: string | (number | string)[]): any

 hasError(errorCode: string, path?: string | (number | string)[]): boolean

So, we can just call this method as usual in get.

Expected behavior

Instead of formGroup.hasError('required', ['x', 'y', 'z']) we can have formGroup.hasError('required', 'x.y.z') for example (as we can call in get method).

What is the motivation / use case for changing the behavior?

More flexibility.