Moved vercelSynvEnvVars to code and updated core.ts

Author: D-K-P

packages/build/src/extensions/core.ts

@@ -3,3 +3,4 @@ export * from "./core/additionalPackages.js";
 export * from "./core/syncEnvVars.js";
 export * from "./core/aptGet.js";
 export * from "./core/ffmpeg.js";
+export * from "./core/vercelSyncEnvVars.js";