Fix coalesced-events test at fractional device pixel ratios

[calixteman]

Firefox can snap dispatched pointer coordinates to device pixels at fractional ratios. Construct mocked samples relative to the actual dispatched event.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.10%. Comparing base (416335a) to head (4dbcba2).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21758      +/-   ##
==========================================
- Coverage   90.10%   90.10%   -0.01%     
==========================================
  Files         264      264              
  Lines       67230    67230              
==========================================
- Hits        60579    60576       -3     
- Misses       6651     6654       +3     

Flag	Coverage Δ
integrationtest	69.32% <ø> (-0.01%)	⬇️
unittestcli	56.58% <ø> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[timvandermeij]

Thanks!