[Swift] Moves capacity outside of Storage (#8650)

- Cleans up capacity usage within the lib and moves it outside of the Storage

-  Use overflow operators

swift/Sources/FlexBuffers/Utils/functions.swift

@@ -117,9 +117,9 @@ func toFixedTypedVectorElementType(type: FlexBufferType)
   let fixedType: UInt64 = numericCast(
     type.rawValue &- FlexBufferType.vectorInt2
       .rawValue)
-  let len: Int = numericCast((fixedType / 3) + 2)
+  let len: Int = numericCast(fixedType.dividedReportingOverflow(by: 3).partialValue &+ 2)
   return (
-    FlexBufferType(rawValue: (fixedType % 3) + FlexBufferType.int.rawValue),
+    FlexBufferType(rawValue: (fixedType.quotientAndRemainder(dividingBy: 3).remainder) &+ FlexBufferType.int.rawValue),
     len)
 }