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

tests/swift/fuzzer/Package.swift

@@ -0,0 +1,35 @@
+// swift-tools-version:5.9
+/*
+ * Copyright 2020 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import PackageDescription
+
+let package = Package(
+  name: "fuzzer",
+  platforms: [
+    .iOS(.v12),
+    .macOS(.v10_14),
+  ],
+  dependencies: [
+    .package(path: "../../.."),
+  ],
+  targets: [
+    .executableTarget(
+      name: "fuzzer",
+      dependencies: [
+        .product(name: "FlatBuffers", package: "flatbuffers"),
+      ]),
+  ])