refactor: migrate on message api for postcss-icss-plugin

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

Full migration on message api

Breaking Changes

No

Additional Info

No

[codecov]

Codecov Report

Merging #838 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #838      +/-   ##
==========================================
- Coverage   99.74%   99.74%   -0.01%     
==========================================
  Files          10       10              
  Lines         396      395       -1     
  Branches       95       97       +2     
==========================================
- Hits          395      394       -1     
  Misses          1        1

Impacted Files	Coverage Δ
lib/plugins/postcss-icss-parser.js	100% <100%> (ø)	⬆️
lib/loader.js	100% <100%> (ø)	⬆️

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