completion-tool list-executables should list executable names (#8053)

Update the completion tool so it prints the list of executable names
instead of target names. The executable products names determines the
name fo the actual binary written to disk, which is what you'd want from
a completion-tool.

That patch also adds a few tests for completion-tool around this
specific behaviour. There weren't existing tests for the
completion-tool. More tests to follow in a subsequent PR focusing on
testing this area specifically.

Fixes #8033

Author: plemarquand

Fixtures/Miscellaneous/DifferentProductTargetName/Package.swift

@@ -0,0 +1,12 @@
+// swift-tools-version:5.2
+import PackageDescription
+
+let package = Package(
+    name: "Foo",
+    products: [
+        .executable(name: "Foo", targets: ["Bar"]),
+    ],
+    targets: [
+        .target(name: "Bar", path: "./"),
+    ]
+)

Fixtures/Miscellaneous/DifferentProductTargetName/main.swift

@@ -76,7 +76,7 @@ extension SwiftPackageCommand {
             case .listExecutables:
                 let graph = try await swiftCommandState.loadPackageGraph()
                 let package = graph.rootPackages[graph.rootPackages.startIndex].underlying
-                let executables = package.modules.filter { $0.type == .executable }
+                let executables = package.products.filter { $0.type == .executable }
                 for executable in executables {
                     print(executable.name)
                 }

Sources/Commands/PackageCommands/CompletionCommand.swift

@@ -551,6 +551,20 @@ final class PackageCommandTests: CommandsTestCase {
         }
     }
 
+    func testCompletionToolListExecutables() async throws {
+        try await fixture(name: "Miscellaneous/MultipleExecutables") { fixturePath in
+            let result = try await execute(["completion-tool", "list-executables"], packagePath: fixturePath)
+            XCTAssertEqual(result.stdout, "exec1\nexec2\n")
+        }
+    }
+
+    func testCompletionToolListExecutablesDifferentNames() async throws {
+        try await fixture(name: "Miscellaneous/DifferentProductTargetName") { fixturePath in
+            let result = try await execute(["completion-tool", "list-executables"], packagePath: fixturePath)
+            XCTAssertEqual(result.stdout, "Foo\n")
+        }
+    }
+
     func testShowExecutables() async throws {
         try await fixture(name: "Miscellaneous/ShowExecutables") { fixturePath in
             let packageRoot = fixturePath.appending("app")