Fix verbalization of Flutter logos in search results page

[atsansone]

From https://buganizer.corp.google.com/issues/337307320

Observed Results

Navigating through the page specifically on the flutter buttons, listen to how are verbalized by SR.

• Screencast VoiceOver
• Screencast ChromeVox

Expected Results

Ensure that the flutter button should have the correct label that is a button opening a new window/tab.

Example: Flutter button that opens the use of memory in a new window/tab.

User Impact

Screen reader and Cognitive users are affected because those buttons are announced as images and never indicate that open a new window/tab.

Steps to Reproduce

1. Enabled VoiceOver using Command + F5 also ChromeVox using Ctrl + Alt + Z
2. Open the following page: https://docs.flutter.dev/search?q=devtools
3. Continue the linear navigation using the Tab key and reach the flutter buttons.
4. Listen that they are announced as thumbnail images and never notified that open a new window/tab.

GAR Assessment

Flutter Docs

GAR Details

1.11. Is the purpose of each link, control, and button clear?

Environment Details

Machine: MAC/ChromeBook
Browser: Chrome Version 120.0.6099.272 (Official Build) (64-bit)
Screen reader: VoiceOver / ChromeVox.
Bug filling time: 15 mins.