Tray: SDL_GetTrayEntries caller-owned pointer, dark mode support on Windows

[Semphriss]

Description

This fixes two issues with the system tray:

• Windows now properly supports dark mode for the context menu.
• SDL_GetTrayEntries returns a caller-owned pointer (it simply duplicates the internal list).

Existing Issue(s)

Fixes #11787

[slouken]

Why isn't nEntries int?

[Semphriss]

Originally, it was because nEntries couldn't be negative and it avoided casts when mixing it with memory/addressing-related functions. I did expose the size parameters as int in the interface though, so I can change it to int if necessary. (Alternatively, I can change the parameters to be size_t, but I'm not sure if size_t is an acceptable type to have in the API)

[slouken]

Can you separate out the dark mode fix into a separate PR?

Thinking more about the memory management of the tray API, we usually return a copy of an array of IDs when the underlying objects can change out from under the user. Displays, joysticks, etc. all fall under this category. Returning a copy of an array of pointers doesn't actually make it any safer, because if the underlying data changes, you're left with a dangling pointer that can crash if you dereference it.

I think it's actually safer to just return a const, NULL terminated, array of pointers, like you did before (with the addition of NULL termination).

@icculus, am I missing anything here?

[icculus]

Agreed. Unlike unplugging a USB joystick, these shouldn't change outside of the app doing it itself.

[Semphriss]

I've reverted the changes and made a new commit that just adds the NULL-termination of the lists; I'll open another PR for the dark theme now.

[slouken]

Looks great, thanks!