Accept custom error message in Validators.pattern()

### Which @angular/* package(s) are relevant/related to the feature request?

forms

### Description

Currently, `Validators.pattern()` is defined as so:

```
static pattern(pattern: string | RegExp): ValidatorFn;
```
When used and the control is invalid we get this as result:

```
pattern: {
requiredPattern: '/^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z]).{6,32}$/',
actualValue: 'hello'
}
```

Right now we can't assign a specific error message to that validator and we always need to use controlName + error type to display the error for the users.

### Proposed solution

The proposed solution is to accept a secondary parameter, with a custom error message and return that message along with the rest of the error data:

```
static pattern(pattern: string | RegExp, message: string | undefined): ValidatorFn;
```

### Alternatives considered

Perhaps this would be beneficial as well to be added to other types of Validators.

Start in the Angular forms package at the Validators.pattern() entry point and inspect how its validation error data is assembled. Compare related validator APIs and their tests, then verify that the proposed custom message is returned with the existing pattern error data without changing current behavior.

Written by the indexing model from the issue text.