Add a Swift 6 toolchain Package.swift

And enable Swift 6 mode.
But the new Xcode throws a lot of deprecation
warnings.

Package@swift-6.swift

@@ -0,0 +1,119 @@
+// swift-tools-version:6.0
+
+import PackageDescription
+
+var package = Package(
+  name: "Lighter",
+
+  platforms: [ .macOS(.v10_15), .iOS(.v13) ],
+
+  products: [
+    .library(name: "Lighter",         targets: [ "Lighter"       ]),
+    .library(name: "SQLite3Schema",   targets: [ "SQLite3Schema" ]),
+
+    .executable(name: "sqlite2swift", targets: [ "sqlite2swift"  ]),
+
+    .plugin(name: "Enlighter",        targets: [ "Enlighter"     ]),
+    .plugin(name: "Generate Code for SQLite",
+            targets: [ "Generate Code for SQLite" ])
+  ],
+
+  targets: [
+    // A small library used to fetch schema information from SQLite3 databases.
+    .target(name: "SQLite3Schema", exclude: [ "README.md" ]),
+
+    // Lighter is a shared lib providing common protocols used by Enlighter
+    // generated models and such.
+    // Note that Lighter isn't that useful w/o code generation (i.e. as a
+    // standalone lib).
+    .target(name: "Lighter"),
+
+
+    // MARK: - Plugin Support
+
+    // The CodeGenAST is a small and hacky helper lib that can format/render
+    // Swift source code.
+    .target(name    : "LighterCodeGenAST",
+            path    : "Plugins/Libraries/LighterCodeGenAST",
+            exclude : [ "README.md" ]),
+
+    // This library contains all the code generation, to be used by different
+    // clients.
+    .target(name         : "LighterGeneration",
+            dependencies : [ "LighterCodeGenAST", "SQLite3Schema" ],
+            path         : "Plugins/Libraries/LighterGeneration",
+            exclude      : [ "README.md", "LighterConfiguration/README.md" ]),
+
+
+    // MARK: - Tests
+
+    .testTarget(name: "CodeGenASTTests", dependencies: [ "LighterCodeGenAST" ]),
+    .testTarget(name: "EntityGenTests",  dependencies: [ "LighterGeneration" ]),
+    .testTarget(name: "LighterOperationGenTests",
+                dependencies: [ "LighterGeneration" ]),
+    .testTarget(name: "ContactsDatabaseTests", dependencies: [ "Lighter" ],
+                exclude: [ "contacts-create.sql" ]),
+
+
+    // MARK: - Plugins and supporting Tools
+
+    .executableTarget(name         : "sqlite2swift",
+                      dependencies : [ "LighterGeneration" ],
+                      path         : "Plugins/Tools/sqlite2swift",
+                      exclude      : [ "README.md" ]),
+
+    .plugin(name: "Enlighter", capability: .buildTool(),
+            dependencies: [ "sqlite2swift" ]),
+
+    .plugin(
+      name: "Generate Code for SQLite",
+      capability: .command(
+        intent: .custom(
+          verb: "sqlite2swift",
+          description:
+            "Generate Swift code for SQLite DBs into the Sources directory."
+          ),
+          permissions: [
+            .writeToPackageDirectory(reason:
+              "The plugin needs access to generate the source file.")
+          ]
+        ),
+        dependencies: [ "sqlite2swift" ],
+        path: "Plugins/GenerateCodeForSQLite"
+    ),
+
+
+    // MARK: - Internal Plugin for Generating Variadics
+
+    .executableTarget(name         : "GenerateInternalVariadics",
+                      dependencies : [ "LighterCodeGenAST",
+                                       "LighterGeneration" ],
+                      path         : "Plugins/Tools/GenerateInternalVariadics",
+                      exclude      : [ "README.md" ]),
+    .plugin(
+      name: "Generate Variadics into Lighter (Internal)",
+      capability: .command(
+        intent: .custom(
+          verb: "write-internal-variadics",
+          description:
+            "Generate the variadic queries into the Sources/Lighter directory."
+        ),
+        permissions: [
+          .writeToPackageDirectory(
+            reason: "The plugin needs access to generate the source file.")
+        ]
+      ),
+      dependencies: [ "GenerateInternalVariadics" ],
+      path: "Plugins/WriteInternalVariadics"
+    ),
+
+
+    // MARK: - Environment specific tests
+    .testTarget(name: "FiveThirtyEightTests",
+                dependencies: [ "LighterGeneration" ]),
+    .testTarget(name: "NorthwindTests",
+                dependencies: [ "LighterGeneration" ])
+  ],
+
+  swiftLanguageVersions: [ .v5, .v6 ]
+)