The core/vendor directory is for third-party vendor code kept in its original shipped form. Since its contents are auto-generated using Composer and it contains only PHP code, some Drupal core would like for it to only contain that PHP; additionally, they'd like the ability to make the entire folder inaccessible from the webroot.
However, there are 3rd party vendor could that must be web accessible, such as jQuery, Normalize.css, etc. And we are frequently seeing patches that try to update that code to Drupal coding standards.
We need to separate those 3rd party asset files from the rest of Drupal's code base.
Move 3rd party vendor code from core/misc to core/assets/vendor.
The rationale for using "core/assets/vendor" is currently summarized in comment #24.
Move the reset of core/misc into various core/assets/css, core/assets/js, and core/assets/images folders.
User interface changes
No user interfaces are changed.
No API changes are made as the paths are handled by system_library_info().
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