Add blog link to site switcher (#6961)

This makes it more consistent with other Dart-related site properties.
It is still linked to from the top navigation as well.

**Screenshot with the added button:**
<img height="240" alt="Screenshot of the added link button to the blog."
src="https://github.com/user-attachments/assets/32a23cf9-e2a2-48d5-b9bf-bd79a9428f1d"
/>

Author: parlough

site/lib/_sass/components/_dropdown.scss

@@ -13,7 +13,7 @@
     z-index: var(--site-z-dropdown);
 
     .dropdown-divider {
-      background-color: var(--site-outline-variant);
+      background-color: var(--site-outline);
       border-radius: 0.5rem;
       height: 0.125rem;
       margin: 0.25rem;

site/lib/_sass/components/_site-switcher.scss

@@ -44,8 +44,8 @@
     }
 
     &.subtype {
-      padding: 0 0.3rem;
-      font-size: 1.25rem;
+      padding: 0.05rem 0.3rem;
+      font-size: 1.2rem;
       font-weight: 500;
       line-height: 1.3;
       border-radius: 0.25rem;

site/lib/src/components/layout/site_switcher.dart

@@ -36,6 +36,16 @@ final class SiteSwitcher extends StatelessComponent {
                   subtype: 'API',
                   href: 'https://api.dart.dev',
                 ),
+                _SiteWordMarkListEntry(
+                  name: 'Dart',
+                  subtype: 'Blog',
+                  href: 'https://blog.dart.dev',
+                ),
+                Component.element(
+                  tag: 'li',
+                  classes: 'dropdown-divider',
+                  attributes: {'aria-hidden': 'true', 'role': 'separator'},
+                ),
                 _SiteWordMarkListEntry(
                   name: 'DartPad',
                   href: 'https://dartpad.dev',

site/lib/src/style_hash.dart

@@ -2,4 +2,4 @@
 // dart format off
 
 /// The generated hash of the `main.css` file.
-const generatedStylesHash = 'EcoGkjHB12Fs';
+const generatedStylesHash = 'zGgBgeW5Ot3f';