perf(Modal): reduce unnecessary layout invalidations

[HighCoordination]

Improve performance especially in IE11 when a modal is used

[welcome]

💖 Thanks for opening this pull request! 💖

Here is a list of things that will help get it across the finish line:

• Run yarn lint locally to catch formatting errors. This will fix some errors automatically, commit and push any changes.
• Run yarn test locally to catch errors. This ensures all components still behave as they should.
• Run yarn start to run the doc site locally and try a few pages, ensuring everything is in good working order.
• Include tests when adding/changing behavior.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@30d93a3). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master    #3609   +/-   ##
=========================================
  Coverage          ?   99.81%           
=========================================
  Files             ?      174           
  Lines             ?     2745           
  Branches          ?        0           
=========================================
  Hits              ?     2740           
  Misses            ?        5           
  Partials          ?        0

Impacted Files	Coverage Δ
src/modules/Modal/Modal.js	100% <100%> (ø)

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[welcome]

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