fix(windows): hotkeys correctly ignore right modifier keys

Fixes #4619.

The hotkey check in keyman32 would ignore right modifier keys, but the
behaviour was not quite right: it actually needs to take the modifier
into account, but just not treat it as a valid modifier.

While fixing this, I noticed that some of the tests in the
`KeyLanguageSwitchPress` function were using the wrong modifier flags. I
wish I had fewer different modifier flag sets but that ship has probably
sailed.