Allow colons in CSS selectors

Problem/Motivation

When entering classes with colons, like those found in TailwindCSS, a validation error is thrown identical to the one mentioned on this core issue ✨ Allow colons in CSS selectors for CKEditor 5 styles configuration Active

Steps to reproduce

Enter a style for an anchor like a.dark:text-blue-500.

Proposed resolution

Update the selector validation to allow colons.

Remaining tasks

Merge request with a similar fix as for ✨ Allow colons in CSS selectors for CKEditor 5 styles configuration Active to come

User interface changes

None

API changes

None

Data model changes

None