Bring back pnpmfile hack for pnpm/pnpm#3935, which regressed in 9.12.0

Author: anomiex

.pnpmfile.cjs

@@ -223,6 +223,16 @@ function afterAllResolved( lockfile ) {
 		return lockfile;
 	}
 
+	for ( const [ k, v ] of Object.entries( lockfile.packages ) ) {
+		// Forbid installing webpack without webpack-cli. It results in lots of spurious lockfile changes.
+		// https://github.com/pnpm/pnpm/issues/3935
+		if ( k.startsWith( 'webpack@' ) && ! v.optionalDependencies?.[ 'webpack-cli' ] ) {
+			throw new Error(
+				"Something you've done is trying to add a dependency on webpack without webpack-cli.\nThis is not allowed, as it tends to result in pnpm lockfile flip-flopping.\nSee https://github.com/pnpm/pnpm/issues/3935 for the upstream bug report.\n"
+			);
+		}
+	}
+
 	return lockfile;
 }