[Swift] Improving reallocation time by using memcpy and moving reallocation code to storage (#5960)

Removes stride

Use capacity - current size to initialize

Fixes memory leak

Updated test code for linux

tests/FlatBuffers.Test.Swift/Tests/FlatBuffers.Test.SwiftTests/XCTestManifests.swift

@@ -36,6 +36,7 @@ extension FlatBuffersStructsTests {
         ("testCreatingVectorStructWithForcedDefaults", testCreatingVectorStructWithForcedDefaults),
         ("testReadingStruct", testReadingStruct),
         ("testReadingStructWithEnums", testReadingStructWithEnums),
+        ("testWritingAndMutatingBools", testWritingAndMutatingBools),
     ]
 }