Use stripped versions of Standalone Python for Linux

- Introduces minimum target version 0.3.20 for Flatpak and AppImage
  since only newer versions of Standalone Python provided the
  stripped versions.

Author: rmartin16

changes/1929.feature.rst

@@ -0,0 +1 @@
+Apps packaged for Flatpak and AppImage now use a stripped (and smaller) Python support package.

src/briefcase/platforms/linux/__init__.py

@@ -77,7 +77,8 @@ def support_package_url(self, support_revision):
         version, datestamp = support_revision.split("+")
         return (
             "https://github.com/indygreg/python-build-standalone/releases/download/"
-            f"{datestamp}/cpython-{support_revision}-{python_download_arch}-unknown-linux-gnu-install_only.tar.gz"
+            f"{datestamp}/"
+            f"cpython-{support_revision}-{python_download_arch}-unknown-linux-gnu-install_only_stripped.tar.gz"
         )
 
     def vendor_details(self, freedesktop_info):

src/briefcase/platforms/linux/appimage.py

@@ -36,6 +36,7 @@ class LinuxAppImagePassiveMixin(LinuxMixin):
     supported_host_os_reason = (
         "Linux AppImages can only be built on Linux, or on macOS using Docker."
     )
+    platform_target_version = "0.3.20"
 
     def appdir_path(self, app):
         return self.bundle_path(app) / f"{app.formal_name}.AppDir"

src/briefcase/platforms/linux/flatpak.py

@@ -19,6 +19,7 @@ class LinuxFlatpakMixin(LinuxMixin):
     output_format = "flatpak"
     supported_host_os = {"Linux"}
     supported_host_os_reason = "Flatpaks can only be built on Linux."
+    platform_target_version = "0.3.20"
 
     def binary_path(self, app):
         # Flatpak doesn't really produce an identifiable "binary" as part of its