Expose strategies that correspond to string values of runGuardsAndResolvers

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

router

### Description

Given that runGuardsAndResolvers may take a custom strategy in form of a function, it makes sense to expose the set of predefined strategies `'pathParamsChange' | 'pathParamsOrQueryParamsChange' | 'paramsChange' | 'paramsOrQueryParamsChange' | 'always'` so that consumers can compose with them, as was done in case of defaultUrlMatcher, see https://github.com/angular/angular/issues/35928. Also related https://github.com/angular/angular/issues/31843#issuecomment-1890955590

### Proposed solution

Make the strategies part of public api:

```
import { RunGuardsAndResolversStrategies } from '@angular/router';
```

Being:

```
class RunGuardsAndResolversStrategies {
static pathParamsChange() { ... }
static pathParamsOrQueryParamsChange() { ... }
static paramsChange() { ... }
static paramsOrQueryParamsChange() { ... }
static always() { ... }
}
```

### Alternatives considered

Copy paste the code from Angular source code or reimplement said strategies.

Start in the @angular/router implementation of runGuardsAndResolvers and trace how its predefined string strategies are defined and exported through the public router entry point. The work is done when the five strategies are publicly importable as RunGuardsAndResolversStrategies and can be composed by consumers without reimplementing them.

Scritto dal modello di indicizzazione a partire dal testo della issue.