Use babel-plugin-codegen to generate props regex

[emmatown]

What:

Use babel-plugin-codegen to generate the props filter regex instead of babel-plugin-preval.

Why:

So that a regex literal is used instead of a string and then new RegExp()

How:

Use codegen.require and change preval to codegen in all the babel configs

Checklist:

• Documentation N/A
• Tests N/A
• Code complete

[codecov]

Codecov Report

Merging #304 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #304   +/-   ##
=======================================
  Coverage   90.45%   90.45%           
=======================================
  Files          21       21           
  Lines         974      974           
  Branches      261      261           
=======================================
  Hits          881      881           
  Misses         75       75           
  Partials       18       18

Impacted Files	Coverage Δ
packages/react-emotion/src/index.js	100% <100%> (ø)	⬆️

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