HOME button quit screen, with the firmware's art when available

As on a PSP: pressing HOME in a game shows "Do you want to quit the game?"
over it. The game keeps running but gets no input while it's up (sceCtrl
samples are blanked). Left/right picks Yes or No, the confirm button (our
Confirmation button setting, or what compat forces) chooses, the other face
button or HOME closes it, and Yes/No can be tapped. The volume keys change
the game volume a step at a time, shown on the volume bar.

Yes runs the game's registered exit callback first, like the PSP does,
showing "Please wait..." meanwhile. Then, if the XMB launched the game, the
XMB is booted again; otherwise it's back to the game browser, like Exit to
menu. If the callback hasn't ended the game in 10 s, it's quit anyway. Not
in the XMB itself, the PS1 emulator (its own HOME menu) or GE dumps.

It lives in UI/ImposeHome.cpp; EmuScreen only feeds it input and frames and
draws it over the PSP display.

With a firmware dump installed, it's drawn with the firmware's own art from
flash0:/kd/resource/impose.rsc, which is what impose.prx draws it from:
prerendered text for each system language (the question, Yes/No normal and
highlighted, Enter/Back, Please wait...), the button icons, the lines, the
volume bar, the battery and the clock glyphs. The format is documented in
ImposeHome.cpp. Without one, the same screen is drawn with our font and
simple shapes at the same positions.

Where impose.rsc doesn't say where things go, the layout follows
impose_02g.prx (6.61), decrypted and disassembled:
- The screen is filled with 0x9CE7 (#393939); the images are opaque.
- Lines at (80, 96) and (80, 175); impose.prx grows them from the middle
  when it opens, which isn't done here.
- Volume bar: the speaker at (28, 223), 30 steps from x 62, 12 apart. It
  shows our game volume in the PSP's 30 steps.
- Button guide: the cross icon always left, the circle right, "Enter" and
  "Back" next to whichever confirms and cancels.
- Status bar: the battery at (450, 5) (60% and up full, 30% two bars, 12%
  one, then empty), the clock ending next to it at y 5: "M/D H:MM", or
  "D/M" for the DD/MM/YYYY format, no leading zero on the month, day or
  hour, AM/PM for the 12-hour clock.

The clock is the emulated PSP's local time (__RtcGetCurrentLocalTime, new),
in the system's date and time formats. The battery is this device's, since
the emulated PSP's is always full; a device without one shows it full.
For that, Windows now reports -1 for SYSPROP_BATTERY_PERCENTAGE without a
battery (was 100), as SDL already did; SDL polls the battery even when the
status overlay doesn't show it, and the overlay leaves it out when there's
none.

Core side: __CtrlSetGameInputBlocked; __KernelCanExitToVSH and
__KernelRequestExitToVSH to quit to the XMB from outside a syscall; and
__KernelInvokeRegisteredExitCallback(toVSH), so a callback that returns
without exiting ends in the XMB rather than powering down.

New strings: "Do you want to quit the game?", "Please wait..." (Dialog).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NB244iFpvm14JH2FbwHXeQ

Core/HLE/sceKernelModule.cpp

@@ -2762,6 +2762,44 @@ static std::vector<u8> VshmainReturnArgs(const std::vector<u8> &launchArgs) {
 	return args;
 }
 
+// For a game the XMB booted, or loaded in place under its own session: the boot that takes it back
+// to the XMB. False otherwise (or for the XMB itself, or the PS1 emulator, which has its own HOME menu
+// with its own way out).
+static bool GetExitToVSHRequest(BootRequest *request) {
+	if (g_runningVSH || PopsBootActive()) {
+		return false;
+	}
+	const std::optional<VSHLaunch> &launchedFromVSH = PSP_CoreParameter().launchedFromVSH;
+	if (launchedFromVSH) {
+		request->fileToStart = launchedFromVSH->vshmain;
+		request->vshmainArgs = VshmainReturnArgs(launchedFromVSH->vshmainArgs);
+	} else if (PSP_CoreParameter().fileToStart.GetFilename() == "vshmain.prx") {
+		// Loaded in place: the XMB's own boot file is what we started from.
+		request->fileToStart = PSP_CoreParameter().fileToStart;
+		request->vshmainArgs = VshmainReturnArgs(g_vshmainArgs);
+	} else {
+		return false;
+	}
+	request->mountIso = __UmdGetPath();
+	return true;
+}
+
+bool __KernelCanExitToVSH() {
+	BootRequest request;
+	return GetExitToVSHRequest(&request);
+}
+
+bool __KernelRequestExitToVSH() {
+	BootRequest request;
+	if (!GetExitToVSHRequest(&request)) {
+		return false;
+	}
+	INFO_LOG(Log::sceModule, "Quitting the game: back to the XMB");
+	// Stops the core; the frontend then boots the XMB like anything else.
+	PSP_RequestBoot(request);
+	return true;
+}
+
 bool __KernelExitToVSH(MIPSState *mips) {
 	// Normally the XMB launched this game by booting it, so it boots the XMB again.
 	const std::optional<VSHLaunch> &launchedFromVSH = PSP_CoreParameter().launchedFromVSH;