Add missing imports for swiftpm in the products class

Author: shahmishal

utils/swift_build_support/swift_build_support/products/benchmarks.py

@@ -14,6 +14,7 @@
 import platform
 
 from . import product
+from . import swiftpm
 from .. import shell
 from .. import targets
 

utils/swift_build_support/swift_build_support/products/indexstoredb.py

@@ -13,6 +13,7 @@
 import os
 
 from . import product
+from . import swiftpm
 from .. import shell
 from .. import targets
 

utils/swift_build_support/swift_build_support/products/skstresstester.py

@@ -17,6 +17,7 @@
 from build_swift.build_swift.constants import MULTIROOT_DATA_FILE_PATH
 
 from . import product
+from . import swiftpm
 from .. import shell