Ensure classes containing number followed by dash or underscore are extracted correctly (#16980)

Fixes #16978, and also added support for dash.
Classes like `text-theme1-primary` or `text-theme1_primary` should be
treated as valid.

If this approach is not aligned with the project’s direction or there
are any concerns, please feel free to close or edit this PR 😃

<br/>

### As is

Classes conatining number followed by dash or underscore (e.g.
`bg-theme1-primary`, `text-title1_strong`) are ignored, and utility
classes are not generated.

### To be

Classes conatining number followed by dash or underscore (e.g.
`bg-theme1-primary`, `text-title1_strong`) are treated as valid
tailwindcss classes

---------

Co-authored-by: Philipp Spiess <hello@philippspiess.com>