Change icons package directories to match icon-svg repo

Change the following folders:

`information-dense` => `16px`
`regular` => `24px`

Update the icons build script for the changes, but the output should not affect `icons` export.

Find the icons build script and inspect how it maps the current information-dense and regular directories. Rename those directories to 16px and 24px, update the build configuration, and verify that the generated output does not change the icons export.

Written by the indexing model from the issue text.