feat: Introduced @lingui/snowpack-plugin

[semoal]

Introduced @lingui/snowpack-loader. Let's snowpack users compile on the fly his catalogs (the same as @lingui/loader)

Alright is almost ready!

• Pending docs

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[codecov]

Codecov Report

Merging #947 (7d1dffd) into main (8ac50ab) will increase coverage by 0.50%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #947      +/-   ##
==========================================
+ Coverage   82.99%   83.50%   +0.50%     
==========================================
  Files          52       53       +1     
  Lines        1582     1600      +18     
  Branches      427      428       +1     
==========================================
+ Hits         1313     1336      +23     
+ Misses        162      154       -8     
- Partials      107      110       +3     

Impacted Files	Coverage Δ
packages/cli/src/api/catalog.ts	83.73% <ø> (+2.39%)	⬆️
packages/snowpack-plugin/src/index.ts	100.00% <100.00%> (ø)

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[github-actions]

Size Change: 0 B

Total Size: 7.42 kB

ℹ️ View Unchanged

Filename	Size	Change
./packages/core/build/cjs/core.production.min.js	2.09 kB	0 B
./packages/core/build/cjs/dev.production.min.js	2.09 kB	0 B
./packages/detect-locale/build/cjs/detect-locale.production.min.js	961 B	0 B
./packages/react/build/cjs/react.production.min.js	2.28 kB	0 B

_{compressed-size-action}

[amankkg]

Regarding package name. Snowpack and its community are using snowpack-plugin-xyz or @xyz/snowpack-plugin naming template.
Maybe we can also align to it? To me, it seems like xyz-loader is something specific to webpack

[amankkg]

LGTM

Just left some suggestions