Improve AnchorMode_End_LargeAppendAtBottom_StillFollows

[ilonatommy]

The existing AnchorMode_End_LargeAppendAtBottom_StillFollows E2E test did not actually verify auto-follow behavior. Its assertion re-scrolled the container to the bottom inside the polling loop.

Because the test itself performed the scroll-to-bottom that the engine is supposed to do on append, the assertion would be always true, whether or not End-mode auto-follow worked. It provided no real regression coverage for the "append at bottom keeps following" behavior it was named for.

The scenario works correctly, I tested it manually. Only the test's logic needs the "manual" scroll removal.

end-large-append.mp4

[Copilot]

Pull request overview

Updates the Blazor virtualization E2E coverage to ensure the AnchorMode_End_LargeAppendAtBottom_StillFollows test actually validates End-mode auto-follow behavior after a large append, rather than forcing the scroll position in the assertion loop.

Changes:

• Removed the test’s manual scrollTop = scrollHeight assignment from the polling assertion so it no longer “makes itself pass.”
• Strengthened the scenario by additionally asserting that real items near the new end of the list (not provider placeholders) are materialized after the append.