Switch to install_wheel in InstallRequirement

This removes one of usages of the overloaded `source_dir` member.

We know the local_file_path must be set at this point because it is set
in the only 3 places that wheels are added to InstallRequirement.

Author: chrahunt

src/pip/_internal/req/req_install.py

@@ -27,7 +27,7 @@
     generate_metadata as generate_metadata_legacy
 from pip._internal.operations.install.editable_legacy import \
     install as install_editable_legacy
-from pip._internal.operations.install.wheel import install_unpacked_wheel
+from pip._internal.operations.install.wheel import install_wheel
 from pip._internal.pyproject import load_pyproject_toml, make_pyproject_path
 from pip._internal.req.req_uninstall import UninstallPathSet
 from pip._internal.utils.deprecation import deprecated
@@ -774,9 +774,10 @@ def install(
             return
 
         if self.is_wheel:
-            install_unpacked_wheel(
+            assert self.local_file_path
+            install_wheel(
                 self.name,
-                self.source_dir,
+                self.local_file_path,
                 scheme=scheme,
                 req_description=str(self.req),
                 pycompile=pycompile,