[Martin Ferret (MartinFerret)]

Fixes #3607

Since TypeScript 6.0, noUncheckedSideEffectImports is on by default, so import "library-name/css" fails with TS2882 when the subpath doesn't end in .css and has no declaration file. A "*.css" wildcard declaration doesn't help, since it doesn't match the specifier.

This PR updates the option's reference page:

• Updates the example error message to the current TS2882 text.
• Adds a section for library authors: ship a .d.css.ts file next to the stylesheet (users need allowArbitraryExtensions, otherwise TS6263), add a "types" condition in "exports" (no user setting needed), or expose a subpath ending in .css.
• Adds two user-side options: declare the specifier in a global .d.ts, or set the option to false when a bundler already validates CSS imports.

The .d.css.ts approach follows the discussion in microsoft/TypeScript#62674.

The paragraph about the default behavior is left as is, since #3563 already updates it. The two PRs touch separate lines and merge without conflict in either order.

Every example was checked with TypeScript 6.0.3 and 7.0.2, with moduleResolution set to bundler and nodenext.