Adds windows swift support (#8622)

Adding support for windows requires the code generations
to add a compiler statement to completely ignore GRPC code
generation on windows

Cleanup the project to use the main Package.swift to run tests
instead of having it separate and includes the imports for GRPC
within it.

Adds windows swift ci

Package.swift

@@ -31,6 +31,7 @@ let package = Package(
       name: "FlexBuffers",
       targets: ["FlexBuffers"]),
   ],
+  dependencies: .dependencies,
   targets: [
     .target(
       name: "FlatBuffers",
@@ -42,6 +43,40 @@ let package = Package(
       path: "swift/Sources/FlexBuffers"),
     .target(
       name: "Common",
-      dependencies: [],
       path: "swift/Sources/Common"),
+    .testTarget(
+      name: "FlatbuffersTests",
+      dependencies: .dependencies,
+      path: "tests/swift/Tests/Flatbuffers"
+    ),
+    .testTarget(
+      name: "FlexbuffersTests",
+      dependencies: ["FlexBuffers"],
+      path: "tests/swift/Tests/Flexbuffers"
+    )
   ])
+
+extension Array where Element == Package.Dependency {
+  static var dependencies: [Package.Dependency] {
+    #if os(Windows)
+    []
+    #else
+    // Test only Dependency
+    [.package(url: "https://github.com/grpc/grpc-swift.git", from: "1.4.1")]
+    #endif
+  }
+}
+
+extension Array where Element == PackageDescription.Target.Dependency {
+  static var dependencies: [PackageDescription.Target.Dependency] {
+    #if os(Windows)
+    ["FlatBuffers"]
+    #else
+    // Test only Dependency
+    [
+      .product(name: "GRPC", package: "grpc-swift"),
+      "FlatBuffers"
+    ]
+    #endif
+  }
+}