fix: prefer scss, sass and css extension in resolving

[alexander-akait]

This PR contains a:

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

Motivation / Use-Case

Prefer scss, sass and css extensions in resolving. Partial #556

Breaking Changes

No

Additional Info

Resolve already return promise, no need pify

[codecov]

Codecov Report

Merging #645 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #645      +/-   ##
==========================================
+ Coverage   97.79%   97.84%   +0.04%     
==========================================
  Files           6        6              
  Lines         136      139       +3     
==========================================
+ Hits          133      136       +3     
  Misses          3        3

Impacted Files	Coverage Δ
lib/loader.js	100% <100%> (ø)	⬆️

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[HairyRabbit]

nice work!
and ..
would the exts configueable or some way If I want to load json or yaml file from scss file

[alexander-akait]

@HairyRabbit out of scope this PR, node-sass and dart-sass doesn't support json/yaml and etc options, so it is out of scope repo