🐛 Prevent double click on iframe during transition, cleanup test

[alanorozco]

• Offset FIE by scrolltop since its position is fixed (cleanup test).
• Prevent re-sending message during transition by setting pointer-events.

[codecov-io]

Codecov Report

Merging #17090 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #17090      +/-   ##
==========================================
- Coverage   77.88%   77.86%   -0.03%     
==========================================
  Files         562      562              
  Lines       41149    41149              
==========================================
- Hits        32050    32039      -11     
- Misses       9099     9110      +11

Flag	Coverage Δ
#integration_tests	36.17% <ø> (+0.03%)	⬆️
#unit_tests	76.9% <ø> (-0.05%)	⬇️

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