fix(renderer): disable devMode for Fela by default

[layershifter]

Fixes #1088.

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When Fela's renderer is in devMode (default before), the insertRule() function uses a de-optimized code path (insertRuleInDevMode.js) for writing style updates to the style nodes. It replaces the text of the style node in the head, opposed to using the browser's optimized CSSStyleSheet.insertRule() method.

It's friendly for development tools because you can edit styles, but it provides wrong development experience for consumers because components are much slower.

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devMode=true

devMode=false

[miroslavstastny]

Not sure I like it, but

[codecov]

Codecov Report

Merging #1090 into master will decrease coverage by 0.01%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #1090      +/-   ##
==========================================
- Coverage   81.77%   81.76%   -0.02%     
==========================================
  Files         701      701              
  Lines        8564     8570       +6     
  Branches     1170     1244      +74     
==========================================
+ Hits         7003     7007       +4     
- Misses       1546     1548       +2     
  Partials       15       15

Impacted Files	Coverage Δ
packages/react/src/lib/felaRenderer.tsx	86.36% <66.66%> (-7.39%)	⬇️

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