fix(babel-preset-app): allow to specify corejs.version as string

[Yihao-G]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

According to the core-js documentation, it's recommended to specify used minor core-js version:

Warning! Recommended to specify used minor core-js version, like corejs: '3.6', instead of corejs: 3, since with corejs: 3 will not be injected modules which were added in minor core-js releases.

More examples in their documentation:

By default, @babel/preset-env with useBuiltIns: 'usage' option only polyfills stable features, but you can enable polyfilling of proposals by proposals option, as corejs: { version: '3.6', proposals: true }.

However, with the current implementation of babel-preset-app, only integers can be set as they are used as the key of coreJsMeta. This PR enables users to specify minor core-js versions by handling minor version string/number.

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly. (PR: #)
• I have added tests to cover my changes (if not applicable, please state why)

  babel-preset-app doesn't have any tests...

• All new and existing tests are passing.

[codecov-commenter]

Codecov Report

Merging #8085 into dev will decrease coverage by 0.07%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##              dev    #8085      +/-   ##
==========================================
- Coverage   68.98%   68.91%   -0.08%     
==========================================
  Files          91       91              
  Lines        3847     3851       +4     
  Branches     1047     1048       +1     
==========================================
  Hits         2654     2654              
- Misses        969      972       +3     
- Partials      224      225       +1     

Flag	Coverage Δ
#unittests	68.91% <0.00%> (-0.08%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/babel-preset-app/src/index.js	0.00% <0.00%> (ø)

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[pi0]

Hi @Yihao-G Actually it is better to use build.corejs option to specify version and we do it by default. Still your PR seems a good fix 👍