Qt: improve trophy manager icons for high dpi setups

[Megamouse]

Added a small simplification to the game list icon logic. I hope this will be slightly faster. If it is slower for some reason then I will revert this commit.
So please test the icon resize in the game list if you have a huge amount of games (normal screen OR high dpi screen).

Added the high dpi improvements that can already be seen in the game list and in the save data manager to the trophy manager.

Added the background icon color that is already used for the game icons to the trophy icons.

Comparison: (Note my custom black background color on the trophy icons)

[Asinin3]

Before:

After:

Nice work, the speed is the same though still takes me around 2:30~ to open the trophy screen for the first time (on my massive game library with probably around 600 trophy entries). Once it's cached into ram then all subsequent runs take around ~30sec to open the list.