Emulation: Fix boot path resolving

* Fix /dev_flash executables path arg. (/host_root is wrong for it)
* Fix usage of /host_root for homebrew applications when it is not mounted, use /app_home.
* Fix path source detection. (don't get fooled by path slashes repetitions, symlinks, '.', ".." and ('\' on Windows))
* Unescape tail of /dev_hdd0 paths.

rpcs3/rpcs3qt/gui_application.cpp

@@ -27,6 +27,7 @@
 #include <QFontDatabase>
 #include <QLibraryInfo>
 #include <QDirIterator>
+#include <QFileInfo>
 
 #include <clocale>
 
@@ -390,6 +391,11 @@ void gui_application::InitializeCallbacks()
 		return localized_emu::get_u32string(id, args);
 	};
 
+	callbacks.resolve_path = [](std::string_view sv)
+	{
+		return QFileInfo(QString::fromUtf8(sv.data(), static_cast<int>(sv.size()))).canonicalFilePath().toStdString();
+	};
+
 	Emu.SetCallbacks(std::move(callbacks));
 }