[Swift] Migrating benchmarks to a newer lib. (#8168)

* Adds Nativestructs pointer push into ByteBuffer

Updates benchmarks & cleanup

Adds native struct vector tests

* Address PR comments

* Add more benchmarks

* Some benchmark cleanup

* Return back to 1M structs

* Tweak Structs benchmark

* Moves swift Benchmarks folder from /tests to /benchmarks

---------

Co-authored-by: Joakim Hassila <jocke@ordo.one>

swift/Sources/FlatBuffers/FlatBufferBuilder.swift

@@ -623,9 +623,7 @@ public struct FlatBufferBuilder {
     startVector(
       structs.count * MemoryLayout<T>.size,
       elementSize: MemoryLayout<T>.alignment)
-    for i in structs.reversed() {
-      _ = create(struct: i)
-    }
+    _bb.push(elements: structs)
     return endVector(len: structs.count)
   }