Drop .stylelintignore in 10.x

Problem/Motivation

Our styleling configuration tries to lint all files matching pattern: **/*.css. This matches both, generated and ungenerated files. We shouldn't lint generated CSS files because they should be only changed by the compiler.

Proposed resolution

I have at least two potential ways to solve this. We could check if the .css file has a PostCSS file associated to it. Another approach would be to add an identifier to generated filenames and to use --ignore-pattern.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet