Fix alignment of the icon with text in new `u-has-icon` utility

It seems that the icons are not exactly aligned properly when using new `u-has-icon` utility.

We should verify if that is correct and adjust if needed.

It's especially true for social icons, that by default use 1.5 rem size instead of 1rem.

More context: https://github.com/canonical/vanilla-framework/pull/4693#issuecomment-1462140812

Search the framework source for the `u-has-icon` utility and its social-icon styles, then review the screenshot and linked pull request comment for context. Reproduce the misalignment, verify behavior with the 1.5rem social icons, and confirm that the corrected rendering is covered by the relevant framework checks.

Written by the indexing model from the issue text.