Include accessible description in all buttons

[atsansone]

Hotlist: https://buganizer.corp.google.com/hotlists/5891206
Bug: https://buganizer.corp.google.com/issues/338105555

Observed Results

Navigating through the menu options, reach the elipsis button besides the message button and listen to the results.

• Screencast VoiceOver
• Screencast ChromeVox
• Screencast
  See aditional information

Expected Results

Ensure that every button in the page should have an accessible description to users.

User Impact

Screen reader and cognitive users are affected because that button does not have a clear purpose to users.

Steps To Reproduce

1. Enabled VoiceOver using Cmd + F5 also ChromeVox using Ctrl + Alt + Z
2. Open the following page: https://dart.dev/codelabs/async-await
3. Start the linear navigation using Tab key.
4. Reach the first box for executing examples codes, (since reaching the other is posible but only by mouse, it is already reported in b/338110557).
5. Notice that there's a button that does not have a clear purpose

GAR Assessment

A11ytracker

GAR Details

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

Additional Information

This issue regarding of link with no clear purpose for SC users can also be observed in the following url: https://dart.dev/language/variables, also an screencast attachment has been added as well. This in order to use this issue and don't make a duplicate within the same tas.

Environment Details

• Machine: macOS/ChromeOS
• Browser: Chrome Version 124.0.6367.92 (Official Build) (arm64) /Version 123.0.6312.132 (Official Build) (64-bit)
• Screen reader: VoiceOver/ChromeVox.
• Bug filling time: 15 mins