HttpResponse responseType Property Support

This commit adds support for the Fetch API's responseType property in HttpResponse and HttpErrorResponse when using HttpClient with the withFetch provider.

This change enhances HttpClient's alignment with the native Fetch API by exposing the response type information that indicates how the browser handled the response based on CORS policies and request mode. This provides developers with valuable insights into the nature of the response they received.

The Change Includes:

• Added responseType property to HttpResponse and HttpErrorResponse classes
• Maintains consistency with the Fetch API specification
• Added comprehensive unit tests to ensure the property is correctly captured and exposed

Motivation / Use Cases

The responseType property provides crucial information about how the browser handled the response based on CORS policies and request configuration:

• CORS Debugging: Understand why certain headers or response data might be inaccessible
• Security Analysis: Identify opaque responses that may indicate cross-origin issues
• Request Mode Validation: Verify that requests are being handled according to the expected CORS mode
• API Compliance: Maintain consistency with the native Fetch API behavior
• Performance Monitoring: Track different response types for analytics and optimization

Examples of New Usage

// Debug CORS issues by checking response type
this.http.get('https://external-api.com/data', { observe: 'response' }).subscribe({
  next: (response) => {
    if (response.responseType === 'opaque') {
      console.warn('Response is opaque - headers and body may not be accessible');
      console.warn('Consider enabling CORS on the server or using a proxy');
    } else if (response.responseType === 'cors') {
      console.log('CORS is properly configured');
      // Safe to access response headers and body
      this.processResponse(response);
    }
  }
});