feat(webpack): allow babel plugins to be defined by function

[danielroe]

This PR allows build.babel.plugins to be a function that receives context and returns Babel plugins.

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

With the new format for babel-polyfills it may be important to pass targets to Babel plugins, which will likely vary by isModern.

So, in line with the current presets configuration, it would be appropriate for plugins to take a function.

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)
• All new and existing tests are passing.

[codecov-commenter]

Codecov Report

Merging #7443 into dev will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev    #7443      +/-   ##
==========================================
+ Coverage   70.23%   70.25%   +0.01%     
==========================================
  Files          88       88              
  Lines        3699     3701       +2     
  Branches     1009     1010       +1     
==========================================
+ Hits         2598     2600       +2     
  Misses        893      893              
  Partials      208      208              

Flag	Coverage Δ
#unittests	70.25% <100.00%> (+0.01%)	⬆️

Impacted Files	Coverage Δ
packages/webpack/src/config/base.js	62.98% <100.00%> (+0.48%)	⬆️

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[clarkdo]

Change looks good, can you please add some unit tests ?

@pi0 This may also needs ts type definition change?

[danielroe]

@clarkdo I'm happy to put a PR into @nuxt/types with the updated type.

[clarkdo]

I think @pi0 is migrating types to core repo now.

[pi0]

Types package is already moved here (#7432). Would be nice also updating it :)