Update Angular documentation (21.0.3)

Author: simon04

lib/docs/scrapers/angular.rb

@@ -100,7 +100,7 @@ def self.handle_redirects(version)
     end
 
     version do
-      self.release = '20.3.4'
+      self.release = '21.0.3'
       self.base_url = 'https://angular.dev/'
       self.root_path = 'overview'
 
@@ -113,6 +113,20 @@ def self.handle_redirects(version)
       include Docs::Angular::Since18
     end
 
+    version '20' do
+      self.release = '20.3.15'
+      self.base_url = 'https://v20.angular.dev/'
+      self.root_path = 'overview'
+
+      options[:follow_links] = true
+      options[:container] = '.docs-app-main-content'
+      options[:fix_urls] = Since18.handle_redirects(self.version)
+
+      html_filters.push 'angular/entries', 'angular/clean_html_v18'
+
+      include Docs::Angular::Since18
+    end
+
     version '19' do
       self.release = '19.2.15'
       self.base_url = 'https://v19.angular.dev/'