[Swift] Optional Scalars Preparation (#6028)

* Perpares swift to take optional scalars + adds optional string helper method + disables linters in generated code

* Small fix for generated code

* Update grpc support to alpha 17 for swift

swift/FlatBuffers.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name             = 'FlatBuffers'
-  s.version          = '0.6.0'
+  s.version          = '0.7.0'
   s.summary          = 'FlatBuffers: Memory Efficient Serialization Library'
 
   s.description      = "FlatBuffers is a cross platform serialization library architected for

swift/Sources/FlatBuffers/FlatBufferBuilder.swift

@@ -395,6 +395,14 @@ public struct FlatBufferBuilder {
         return Offset(offset: _bb.size)
     }
     
+    /// Insets a string into the buffer using UTF8
+    /// - Parameter str: String to be serialized
+    /// - returns: The strings offset in the buffer
+    mutating public func create(string str: String?) -> Offset<String> {
+        guard let str = str else { return Offset() }
+        return create(string: str)
+    }
+    
     /// Inserts a shared string to the buffer
     ///
     /// The function checks the stringOffsetmap if it's seen a similar string before
@@ -441,6 +449,15 @@ public struct FlatBufferBuilder {
         track(offset: push(element: element), at: position)
     }
         
+    /// Adds a value into the buffer of type optional Scalar
+    /// - Parameters:
+    ///   - element: Optional element of type scalar
+    ///   - position: The predefined position of the element
+    mutating public func add<T: Scalar>(element: T?, at position: VOffset) {
+        guard let element = element else { return }
+        track(offset: push(element: element), at: position)
+    }
+        
     /// Pushes the values into the buffer
     /// - Parameter element: Element to insert
     /// - returns: Postion of the Element