[Swift] Inline arrays (#8755)

Implements InlineArrays which allow us to use Flatbuffers arrays within
Structs natively, and also implements FlatbufferVectors as a secondary API
when using mutable Structs

Fixes mutations within fixed sizes arrays

Adds tests and remove inout and mutating from generated objects in favor of borrowing

---------

Co-authored-by: Wouter van Oortmerssen <aardappel@gmail.com>

swift/Sources/FlatBuffers/FlatBufferObject.swift

@@ -69,5 +69,5 @@ public protocol ObjectAPIPacker {
   static func pack(_ builder: inout FlatBufferBuilder, obj: inout T) -> Offset
 
   /// ``unpack()`` unpacks a ``FlatBuffers`` object into a Native swift object.
-  mutating func unpack() -> T
+  func unpack() -> T
 }

swift/Sources/FlatBuffers/String+extension.swift

@@ -88,7 +88,7 @@ extension String: ObjectAPIPacker {
     builder.create(string: obj)
   }
 
-  public mutating func unpack() -> String {
+  public func unpack() -> String {
     self
   }
 

swift/Sources/FlatBuffers/Struct.swift

@@ -48,4 +48,16 @@ public struct Struct {
     let r = bb.read(def: T.self, position: Int(o &+ position))
     return r
   }
+
+  public func vector<T>(
+    at off: Int32,
+    count: Int,
+    size: Int) -> FlatbufferVector<T>
+  {
+    FlatbufferVector(
+      bb: bb,
+      startPosition: position &+ off,
+      count: count,
+      byteSize: size)
+  }
 }

swift/Sources/FlatBuffers/Table.swift

@@ -137,7 +137,6 @@ public struct Table {
     if offset == 0 {
       return 0
     }
-
     return vector(count: offset)
   }