feat: support absolute URL, when experiments.buildHttp enabled

[alexander-akait]

This PR contains a:

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

Motivation / Use-Case

supports absolute URLs

Breaking Changes

No

Additional Info

https://webpack.js.org/configuration/experiments/, now only for url

[codecov]

Codecov Report

Merging #1389 (bf66657) into master (fee0582) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1389      +/-   ##
==========================================
+ Coverage   96.87%   96.95%   +0.07%     
==========================================
  Files          12       12              
  Lines        1089     1115      +26     
  Branches      377      401      +24     
==========================================
+ Hits         1055     1081      +26     
  Misses         25       25              
  Partials        9        9              

Impacted Files	Coverage Δ
src/index.js	100.00% <100.00%> (ø)
src/plugins/postcss-url-parser.js	97.80% <100.00%> (ø)
src/runtime/api.js	100.00% <100.00%> (ø)
src/utils.js	94.72% <100.00%> (+0.12%)	⬆️
src/plugins/postcss-import-parser.js	100.00% <0.00%> (ø)

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