fix(css): ensure order of extracted CSS

Without this the order of the extracted CSS rules is defined by the order `renderChunk` of the css plugin is called.
So with this the order of CSS rules is always in alphabetical order of the output chunks.

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

packages/vite/src/node/plugins/css.ts

@@ -912,7 +912,9 @@ export function cssPostPlugin(config: ResolvedConfig): Plugin {
           css += chunkCSSMap.get(chunk.preliminaryFileName) ?? ''
         }
 
-        for (const chunkName of chunkCSSMap.keys())
+        // sorted chunk names to guarantee output order (deterministic output)
+        const chunkNames = [...chunkCSSMap.keys()].sort()
+        for (const chunkName of chunkNames)
           collect(prelimaryNameToChunkMap.get(chunkName)?.fileName ?? '')
 
         return css