Stylelint: extract the shared rule set into a reusable "project" preset

[i-am-chitti]

What?

Closes #81349

Adds a project preset to @wordpress/stylelint-config holding the Stylelint rules Gutenberg and WordPress Core share, and switches tools/stylelint/config.js over to it so the set has a single source.

Why?

wordpress-develop#12934 proposes adding Stylelint to Core, and its .stylelintrc.js is currently a copy of Gutenberg's config. The overlap is exact: Core's file is tools/stylelint/config.js minus declaration-property-value-disallowed-list, plugin-wpds/no-token-fallback-values and the overrides section — the other ~22 rules and both report*Disables options are identical. Keeping two copies in sync by hand is the maintenance problem the issue describes.

How?

The shared set becomes a fourth preset in the already-published @wordpress/stylelint-config, alongside scss / stylistic / scss-stylistic, rather than a new package. It extends scss-stylistic and carries the shared rules plus reportNeedlessDisables and reportDescriptionlessDisables.

tools/stylelint/config.js drops from 173 to 122 lines and keeps only Gutenberg's own configuration:

extends: '@wordpress/stylelint-config/project',
plugins: [ 'stylelint-plugin-logical-css' ],
rules: { /* wp-components-color / font-weight / cursor only */ },
overrides: [ /* CSS modules + routes/ */ ],

Core's config then becomes extends: '@wordpress/stylelint-config/project' plus its ignorePath.

Two incidental cleanups fall out: the file was re-registering the no-token-fallback-values plugin and re-enabling its rule, both already no-ops given the base config, and tools/stylelint no longer needs its @wordpress/theme dependency.

Note for reviewers: plugin-wpds/no-token-fallback-values is excluded from the extracted set per the issue, but that does not actually keep it out of Core — it is enabled in the base index.js that Core already extends, along with no-unknown-ds-tokens and no-setting-wpds-custom-properties. They are inert there (Core has no --wpds-* tokens), so this PR leaves the base preset alone; excluding WPDS rules from Core entirely would be a separate, more disruptive change.

Testing Instructions

This is a no-op refactor for Gutenberg — the goal is proving the resolved config did not change.

1. npm run lint:css
2. npm run test:unit packages/stylelint-config
3. Optional, to confirm equivalence directly — compare npx stylelint --print-config <file> on this branch against trunk for each file shape in the repo:
   • packages/components/src/button/style.scss (plain SCSS)
   • packages/components/src/angle-picker-control/style.module.scss (CSS module, SCSS)
   • widgets/hello-world/style.module.css (CSS module, CSS)
   • routes/template-list/style.scss (routes/)

Output is semantically identical for all four; only key ordering shifts, so sort keys before diffing.

Testing Instructions for Keyboard

N/A — build tooling only, no UI changes.

Use of AI

Claude Code Opus 5
Purpose - compare configs, extract shared rules, verify equivalence, write tests