Revert: Remove the validation packages from public products (apple#287)

Author: erikbasargin

Package.swift

@@ -36,7 +36,10 @@ let availabilityMacros: [SwiftSetting] = versionNumbers.flatMap { version in
 let package = Package(
   name: "swift-async-algorithms",
   products: [
-    .library(name: "AsyncAlgorithms", targets: ["AsyncAlgorithms"])
+    .library(name: "AsyncAlgorithms", targets: ["AsyncAlgorithms"]),
+    .library(name: "AsyncSequenceValidation", targets: ["AsyncSequenceValidation"]),
+    .library(name: "_CAsyncSequenceValidationSupport", type: .static, targets: ["AsyncSequenceValidation"]),
+    .library(name: "AsyncAlgorithms_XCTest", targets: ["AsyncAlgorithms_XCTest"]),
   ],
   targets: [
     .target(