Fix save list, delete save, exit without saving, and blank username on Windows64 (#539)

* Fix world save rename not applying new name

KeyboardCompleteWorldNameCallback had no _WINDOWS64 branch, so the
typed name was validated then silently discarded on every rename attempt.

Write the new name to a worldname.txt sidecar file next to the save
(Windows64\GameHDD\{folder}\worldname.txt) and update the in-memory
display name immediately. ReadLevelNameFromSaveFile now checks for this
sidecar first so renamed saves persist correctly across restarts.

* Fixed gamertag being blank upon renaming and re-joining a save

* Save deletion fix, exiting without saving fix

* Add native in-game keyboard UI for world naming and renaming

Minecraft.Client/Windows64/Windows64_Minecraft.cpp

@@ -565,6 +565,12 @@ LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
 		g_KBMInput.SetWindowFocused(true);
 		break;
 
+	case WM_CHAR:
+		// Buffer typed characters so UIScene_Keyboard can dispatch them to the Iggy Flash player
+		if (wParam >= 0x20 || wParam == 0x08 || wParam == 0x0D) // printable chars + backspace + enter
+			g_KBMInput.OnChar((wchar_t)wParam);
+		break;
+
 	case WM_KEYDOWN:
 	case WM_SYSKEYDOWN:
 	{