pw_build: Include Python setup sources in _package_metadata

This will trigger the build venv to regenerate the requirements.txt
and install new packages.

Bug: b/240734482
Change-Id: Ie180ce745d6ba8449b5fce73a5e079a1a038f9ac
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/103888
Reviewed-by: Armando Montanez <[email protected]>
Commit-Queue: Anthony DiGirolamo <[email protected]>
Pigweed-Auto-Submit: Anthony DiGirolamo <[email protected]>

pw_build/python.gni

@@ -383,12 +383,24 @@ template("pw_python_package") {
     # Finally, write out the json
     write_file(_package_metadata_json_file, _package_metadata, "json")
 
-    # Create a target group for the Python package metadata only.
-    group("$target_name._package_metadata") {
+    # Create a target group for the Python package metadata only. This is a
+    # python_action so the setup sources can be included as inputs.
+    pw_python_action("$target_name._package_metadata") {
       metadata = {
         pw_python_package_metadata_json = [ _package_metadata_json_file ]
       }
 
+      script = "$dir_pw_build/py/pw_build/nop.py"
+
+      if (_generate_package) {
+        inputs = [ "$_setup_dir/setup.json" ]
+      } else {
+        inputs = _setup_sources
+      }
+
+      _pw_internal_run_in_venv = false
+      stamp = true
+
       # Forward the package_metadata subtarget for all python_deps.
       public_deps = []
       foreach(dep, _python_deps) {

pw_build/python_venv.gni

@@ -149,7 +149,7 @@ template("pw_python_venv") {
       ]
 
       outputs = [ _generated_requirements_file ]
-      deps = [ ":${invoker.target_name}._create_virtualenv($pw_build_PYTHON_TOOLCHAIN)" ]
+      deps = _pkg_gn_labels + [ ":${invoker.target_name}._create_virtualenv($pw_build_PYTHON_TOOLCHAIN)" ]
     }
   } else {
     group("${target_name}._generate_3p_requirements") {