fix(launcher): only remove launcher artifacts this project created

Match the legacy entry against this checkout's desktop-run.sh instead of any
desktop-run.sh, and delete the legacy icon files only after that entry or the
old artwork proves ownership.  Quote and escape Exec arguments as the Desktop
Entry specification requires, so a checkout path with reserved characters no
longer produces an invalid entry, and escape the Path value.

Use StartupWMClass=RiotClientServices in both entries: Darling derives WM_CLASS
from -[NSProcessInfo processName], the basename of argv[0], and the launcher
starts .../RiotClientServices.  "Riot Client" is only the bundle display name,
so the checkout entry never matched the window.  Both entries now share
Name/GenericName/Comment/Icon/Keywords/Categories and a test keeps them in
sync; Terminal stays different because the checkout entry logs to
build/desktop-launch.log while the packaged entry runs the session in a
terminal.

Also drop the stray top-level icon copies, handle dangling legacy symlinks,
name the icon for assistive technology, document the alias and menu entry, and
cover the helper with disposable-HOME tests.

.github/workflows/source-check.yml

@@ -25,6 +25,7 @@ jobs:
       - run: python -m unittest discover -s tests -p 'test_nix_repairs.py'
       - run: python -m unittest discover -s tests -p 'test_hidden_riot_recovery.py'
       - run: python -m unittest discover -s tests -p 'test_desktop_run.py'
+      - run: python -m unittest discover -s tests -p 'test_desktop_entry.py'
       - run: python -m unittest discover -s tests -p 'test_urlsession_runner.py'
       - run: python -m unittest discover -s tests -p 'test_system_profiler.py'
       - run: python -m unittest discover -s tests -p 'test_metal_device_info.py'