Set the icon on window regeneration

[weirddan455]

Description

The icon currently gets lost when the window is regenerated. To reproduce:

1. Type fullscreen=true into Dosbox (doesn't work but it still regenerates the window, changing any other setting in the [sdl] group should also suffice).
2. Icon goes missing in both the top left of the window and at the bottom where the open windows are shown. On KDE, it gets replaced by a default Xorg icon.

Note, this is probably not reproducible on Mac or MSVC builds as those don't have an empty SetIcon function:

dosbox-staging/src/gui/sdlmain.cpp

Lines 534 to 544 in e91cae4

	/* On macOS, as we use a nicer external icon packaged in App bundle.
	*
	* Visual Studio bundles .ico file specified in winres.rc into the
	* dosbox.exe file.
	*
	* Other OSes will either use svg icon bundled in the native package, or
	* the window uploaded via SDL_SetWindowIcon below.
	*/
	#if defined(MACOSX) || defined(_MSC_VER)
	static void SetIcon() {}
	#else

The fix is to move the SetIcon() call into the set_output function. This gets called in both the inital startup and when the window gets regenerated. Also moved setting the window title in there for good measure (this gets re-set later anyway to show cycles/ms so it probably doesn't matter much).

Manual testing

Confirmed icon and window title are getting set properly and stay set after a window regeneration.

Checklist

Please tick the items as you have addressed them. Don't remove items; leave the ones that are not applicable unchecked.

I have:

• followed the project's contributing guidelines and code of conduct.
• performed a self-review of my code.
• commented on the particularly hard-to-understand areas of my code.
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• confirmed that my code does not cause performance regressions (e.g., by running the Quake benchmark).
• added unit tests where applicable to prove the correctness of my code and to avoid future regressions.
• made corresponding changes to the documentation or the website according to the documentation guidelines.
• locally verified my website or documentation changes.

[kcgen]

(just a small suggestion)
Nice catch, @weirddan455 !