Read and write shortcut ids to vdf to fix downloaded art

[idbrii]

Read and write shortcut ids to vdf

Fix #37: Downloaded art no longer displays in Steam.

Valve changed how Steam identifies art. Instead of hashing the exe and name, it generates a shortcut id and stores it in shortcuts.vdf as 'appid'. Presumably this is so art is preserved when renaming shortcuts.

We can't wait for steam to populate the shortcut_id for our newly added shortcuts, so instead we use the old method to generate a shortcut_id and write it into the vdf. After removing other shortcuts and multiple restarts of Steam, it seems that this method reliably and permanently sets a shortcut id.

Also use the new name format for big picture art. It now matches the id format of the others.

Test

• Use steamsync to add 4 shortcuts from Xbox with art and they all show up. Remove one from within Steam and restart. The other three still have their art.
• Use steamsync to add a bunch of epic and itchio shortcuts and their art looks correct art except itchio ones using gifs (which aren't supported by steam).

Also adds a --dump-shortcut-vdf argument which is helpful to debug this kind of issue.

Also handles "Win10" suffix on games when detecting appid. I was testing with Death's Door and it wasn't detected correctly.

[jaydenmilne]

You're a hero for doing this