Use new this() instead of new OAuth2Strategy() in the static discover() function

[ezraripps]

This solves an issue where strategies that extend OAuth2Strategy cannot use the discover() method, as it will construct the base class and not the one extending it.

export class CustomOauthStrategy extends OAuth2Strategy {
	protected authorizationParams(params: URLSearchParams): URLSearchParams {
	  	params.set('custom_param', 'value');
	  	return(params);
	}
}

const strategy = await CustomOauthStrategy.discover(...); // This will be OAuth2Strategy, not CustomOauthStrategy

// Thus, CustomOauthStrategy.authorizationParams will never be called

[ezraripps]

@sergiodxa Any updates?