Centralize and Automate Plugin Asset Minification in Webpack

[ShyamGadde]

Summary

Fixes #1711

This is also an attempt to improve the solution introduced in #1643 by further streamlining the process of generating minified asset files.

Relevant technical choices

• Removed Webpack configurations for Performance Lab, Embed Optimizer, and Image Prioritizer that existed solely for asset minification, making them redundant with the new centralized approach.
• Implemented plugin-specific minification:
  • When running npm run build:plugin:optimization-detective (or any specific plugin), only assets for that plugin are minified.
  • This prevents redundant minification when using npm run build-plugins script, which would otherwise re-minify the same assets multiple times (while the overhead may be minimal, this approach avoids redundancy.)
• When npm run build is executed, it generates minified versions of assets across all plugins.

[github-actions]

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Co-authored-by: ShyamGadde <shyamgadde@git.wordpress.org>
Co-authored-by: westonruter <westonruter@git.wordpress.org>

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[westonruter]

Looking good to me, but someone who is more experienced with webpack than me should review this.

[ShyamGadde]

The reason for adding this is that unit tests for the plugins can fail if the minified assets aren’t generated. Since Webpack is responsible for generating these assets and copying necessary libraries from node_modules to the build, it makes sense to include changes to webpack.config.js as a trigger for the unit tests.