Migrate addon cssresources to TS

[gaetanmaisse]

Issue:

#5030

What I did

• Migrated @storybook/addon-addon-cssresources to TypeScript
• Refactor some class and import/export
• Fix README (an attribute name was wrong: name -> id)

[codecov]

Codecov Report

Merging #5380 into next will increase coverage by 0.1%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             next    #5380     +/-   ##
=========================================
+ Coverage   30.37%   30.48%   +0.1%     
=========================================
  Files         622      620      -2     
  Lines        8957     8927     -30     
  Branches     1229     1245     +16     
=========================================
  Hits         2721     2721             
+ Misses       5579     5561     -18     
+ Partials      657      645     -12

Impacted Files	Coverage Δ
addons/cssresources/src/index.ts	0% <0%> (ø)
addons/cssresources/src/register.tsx	0% <0%> (ø)
addons/cssresources/src/constants.ts	0% <0%> (ø)
lib/theming/src/themes/dark-syntax.ts

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