Tests: remove @testable import Commands

Use the newly extended APIs for testing and use a non-testable import of
the package, avoiding a recompilation.

Author: compnerd

Tests/BuildTests/PrepareForIndexTests.swift

@@ -12,7 +12,7 @@
 
 import Build
 import Foundation
-@testable import Commands
+import Commands
 import CoreCommands
 import LLBuildManifest
 import _InternalTestSupport

Tests/CommandsTests/BuildCommandTests.swift

@@ -12,7 +12,7 @@
 
 import Foundation
 import Basics
-@testable import Commands
+import Commands
 import CoreCommands
 import PackageGraph
 import PackageLoading

Tests/CommandsTests/MermaidPackageSerializerTests.swift

@@ -21,7 +21,6 @@ import struct PackageModel.ProductDescription
 import struct PackageModel.TargetDescription
 import func _InternalTestSupport.XCTAssertNoDiagnostics
 
-@testable
 import Commands
 
 import XCTest

Tests/CommandsTests/PackageCommandTests.swift

@@ -12,7 +12,7 @@
 
 import Basics
 import CoreCommands
-@testable import Commands
+import Commands
 import Foundation
 
 @_spi(DontAdoptOutsideOfSwiftPMExposedForBenchmarksAndTestsOnly)

Tests/CommandsTests/SwiftCommandStateTests.swift

@@ -12,7 +12,7 @@
 
 import Basics
 import Build
-@testable import Commands
+import Commands
 import CoreCommands
 
 @_spi(DontAdoptOutsideOfSwiftPMExposedForBenchmarksAndTestsOnly)