Add regression test for #5728 (#5991)

Author: ncooke3

Fixtures/Resources/FoundationlessClient/UtilsWithFoundationPkg/Package.swift

@@ -0,0 +1,17 @@
+// swift-tools-version:5.8
+import PackageDescription
+
+// This package acts as a regression test for the FoundationlessPackages to
+// assert that Swift targets with resources are not affected by using
+// `@_implementationOnly import Foundation` in the generated resource accessor.
+let package = Package(
+    name: "UtilsWithFoundationPkg",
+    targets: [
+        .target(
+            name: "UtilsWithFoundationPkg",
+            resources: [
+                .copy("foo.txt"),
+            ]
+        )
+    ]
+)

Fixtures/Resources/FoundationlessClient/UtilsWithFoundationPkg/Sources/UtilsWithFoundationPkg/FooUtils.swift

@@ -0,0 +1,8 @@
+import Foundation
+
+@frozen
+public enum FooUtils { }
+
+extension FooUtils {
+  public static let foo: String = "Hello, World!"
+}

Fixtures/Resources/FoundationlessClient/UtilsWithFoundationPkg/Sources/UtilsWithFoundationPkg/foo.txt

@@ -0,0 +1 @@
+foo

Tests/FunctionalTests/ResourcesTests.swift

@@ -116,6 +116,15 @@ class ResourcesTests: XCTestCase {
         }
     }
 
+    func testSwiftResourceAccessorDoesNotCauseInconsistentImportWarning() throws {
+        try fixture(name: "Resources/FoundationlessClient/UtilsWithFoundationPkg") { fixturePath in
+            XCTAssertBuilds(
+                fixturePath,
+                Xswiftc: ["-warnings-as-errors"]
+            )
+        }
+    }
+
     func testResourceBundleInClangPackageWhenRunningSwiftTest() throws {
         #if !os(macOS)
         // Running swift-test fixtures on linux is not yet possible.