Improve Build Log scrolling experience

What does this MR do?

This MR does some minor enhancements to Build Log scrolling experience, which are as follows:

1. Enable Autoscroll automatically when user scrolls to bottom of the build log while build is running, disable Autoscroll when user scrolls back up.
2. Enhance scroll button styling as proposed in issue #19620 (closed).
3. Indicate autoscroll status as text (by removing Enable/Disable autoscroll button), since with point 1. this button is unnecessary.

Are there points in the code the reviewer needs to double check?

Do we have any method that does the job of isInViewport() method added in build.js ? If so, we can remove this redundant implementation.

Update

isInViewport() is now part of gl.utils.

Why was this MR needed?

See #19620 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #19620 (closed)