fix(link): improve ionic theme links styles and dev experience (#30375)

Issue number: internal

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## What is the new behavior?
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- Adjust link styles to match latest Figma UI and tokens.
- For default link, make it work without the need of adding a class.
- Change `ionic` to `ion` on the class names.
- Adjusted tests to reflect the changes.

## Does this introduce a breaking change?

- [] Yes
- [x] No

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## Other information

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- [Ionic
Link](https://ionic-framework-git-rou-11850-ionic1.vercel.app/src/css/test/link/basic?ionic:theme=ionic)

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Co-authored-by: ionitron <hi@ionicframework.com>

Author: BenOsodrac

core/src/components/list-header/test/basic/index.html

@@ -42,7 +42,7 @@
               Title
               <p>With list + link</p>
             </ion-label>
-            <a class="ionic-link" href="#">Clear</a>
+            <a href="#">Clear</a>
           </ion-list-header>
           <ion-item lines="none">
             <ion-label color="primary">List item</ion-label>