[SyntaxRewriter] Avoid unnecessary work to replace node's parents for SyntaxRewriter

The SyntaxRewriter only needs to collect root nodes to compose together, we don't need to replace the parent hiearchy for these temporary root nodes.

Author: akyrtzi

Sources/SwiftSyntax/SyntaxRewriter.swift.gyb

@@ -95,8 +95,7 @@ open class SyntaxRewriter {
     assert(newLayout.count == node.raw.numberOfChildren)
 
     let newRaw = node.raw.replacingLayout(newLayout)
-    let newData = node.base.data.replacingSelf(newRaw)
-    return makeSyntax(newData)
+    return makeSyntax(.forRoot(newRaw))
   }
 }