Create SwiftSyntax510 module for version indication

Author: Matejkob

Package.swift

@@ -146,7 +146,7 @@ let package = Package(
 
     .target(
       name: "SwiftSyntax",
-      dependencies: ["SwiftSyntax509"],
+      dependencies: ["SwiftSyntax509", "SwiftSyntax510"],
       exclude: ["CMakeLists.txt"],
       swiftSettings: swiftSyntaxSwiftSettings
     ),
@@ -163,6 +163,11 @@ let package = Package(
       dependencies: []
     ),
 
+    .target(
+      name: "SwiftSyntax510",
+      dependencies: []
+    ),
+
     // MARK: SwiftSyntaxBuilder
 
     .target(

Sources/SwiftSyntax510/Empty.swift

@@ -0,0 +1,3 @@
+// The SwiftSyntax510 module is intentionally empty.
+// It serves as an indicator which version of swift-syntax a package is building against.
+// See the 'Macro Versioning.md' document for more details.