Native addons that hold persistent references to callbacks, emitters,
and threadsafe functions prevent Electron from quitting cleanly since
Electron 40.5.0 due to changes in Node.js shutdown behavior. This adds
a `destroy()` method to all four native code tutorials (Swift macOS,
Obj-C macOS, C++ Linux, C++ Win32) that releases these resources and
must be called before app quit.
The destroy method resets callback and emitter references and aborts the
threadsafe function, allowing the addon's destructor to run properly.
An [!IMPORTANT] note is added to each tutorial's JavaScript wrapper
section explaining when and why to call destroy().
Fixes#50457
Signed-off-by: Asish Kumar <officialasishkumar@gmail.com>
