chore(deps): update

[alexander-akait]

This PR contains a:

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

Motivation / Use-Case

use PostCSS 8

Breaking Changes

Yes

Additional Info

• more perf improvements in plugins
• one regression with url and @value, I think we need to fix it in plugin

[codecov]

Codecov Report

Merging #1208 into master will increase coverage by 0.22%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1208      +/-   ##
==========================================
+ Coverage   99.18%   99.41%   +0.22%     
==========================================
  Files          22       11      -11     
  Lines        1356      679     -677     
  Branches      441      218     -223     
==========================================
- Hits         1345      675     -670     
+ Misses         11        4       -7     

Impacted Files	Coverage Δ
src/plugins/postcss-import-parser.js	100.00% <100.00%> (ø)
src/plugins/postcss-url-parser.js	100.00% <100.00%> (ø)
D:/a/css-loader/css-loader/src/runtime/getUrl.js
...r/css-loader/src/runtime/cssWithMappingToString.js
D:/a/css-loader/css-loader/src/utils.js
D:/a/css-loader/css-loader/src/cjs.js
D:/a/css-loader/css-loader/src/index.js
...ader/css-loader/src/plugins/postcss-icss-parser.js
D:/a/css-loader/css-loader/src/Warning.js
D:/a/css-loader/css-loader/src/CssSyntaxError.js
... and 4 more

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