[Testing] Replace Thread.Sleep with retryTimeout in UI tests

[Copilot]

Applies Copilot code review suggestions from PR #33749 to net11.0. Replaces fixed Thread.Sleep delays with adaptive retryTimeout parameters that retry screenshot comparisons until they match or timeout.

Changes

• 9 UI test files: Replace Thread.Sleep/Task.Delay with retryTimeout parameter
• Issue18751.cs: Add comment explaining CollectionView vs ListView timing differences (addresses Copilot review noting inconsistency with Issue18896)
• Issue10563.cs: Add comment clarifying retryTimeout (not tolerance) for animation timing per UI testing guidelines

Example

// Before
Thread.Sleep(1000);
VerifyScreenshot();

// After
VerifyScreenshot(retryTimeout: TimeSpan.FromSeconds(2));

Files Changed

File	Change
Issue10563	retryTimeout 2s→3s + guideline comment
Issue18751	Task.Delay→retryTimeout + CollectionView timing comment
Issue18857, Issue24856, Issue25192	Thread.Sleep→retryTimeout
Issue27418	Remove #if WINDOWS Sleep, use cross-platform retryTimeout
Issue28657, Issue30575	Thread.Sleep→retryTimeout
Issue18896	Thread.Sleep→retryTimeout + ListView timing comment

Original prompt

Create a PR with the suggestions of copilot review and create a new PR with these changes to nett11.0 branch

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[PureWeen]

@rmarinho

Might be good to grab this one that just got merged to main
#33749