Add platform.freedesktop_os_release() (#6432)

Documented here: https://docs.python.org/3/library/platform.html#linux-platforms

stdlib/platform.pyi

@@ -62,3 +62,6 @@ def python_revision() -> str: ...
 def python_build() -> tuple[str, str]: ...
 def python_compiler() -> str: ...
 def platform(aliased: bool = ..., terse: bool = ...) -> str: ...
+
+if sys.version_info >= (3, 10):
+    def freedesktop_os_release() -> dict[str, str]: ...