Fix stdio with app execution aliases (Microsoft Store applications)

[dscho]

When I introduced support for executing Microsoft Store applications through their "app execution aliases" (i.e. special reparse points installed into %LOCALAPPDATA%\Microsoft\WindowsApps), I had missed that it failed to spawn the process with the correct handles to the terminal, breaking interactive usage of, say, the Python interpreter.

This was later reported on the cygwin mailing list, and also in https://github.com/python/pymanager/issues/210 (which was then re-reported in https://github.com/msys2/MSYS2-packages/issues/1943#issuecomment-3467583078).

The root cause is that the is_console_app() function required quite a bit of TLC, which this here PR tries to provide.

This is a companion of https://github.com/cygwingitgadget/cygwin/pull/5

/cc @ynkdir