[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>

benchmarks/swift/README.md

@@ -0,0 +1,9 @@
+# Benchmarks
+
+To open the benchmarks in xcode use:
+
+`open --env BENCHMARK_DISABLE_JEMALLOC=true Package.swift`
+
+or running them directly within terminal using:
+
+`swift package benchmark`