[desktop] Clean up game list code, fix external watcher crash, and fix macOS flickering (#4106)

- Remove unnecessary icon update code (the UI reloads this stuff anyways); test on Windows please
- Cleaned up a bunch of duplicated/unused code within the game list
- Fix the game list constantly reloading on macOS
  * When you reconstruct the entire directory list on the watcher the directoryChanged signal fires on macOS--seems like a behavioral change that occurred somewhere in the 6.8 release cycle--and it would enter an infinite loop very quickly
  * To fix this, only the differences between the current and old watch list are accounted for on both ends.
  * Since this bug is now fixed, macOS uses Qt 6.11.1 now. Should theoretically improve our situation.
- Fix the external content watcher crashing; the worker would attempt to read files that didn't exist without any bounds since its cache was still pointing to that file.

This supersedes and replaces #4099.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4106
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

CMakeLists.txt

@@ -589,12 +589,7 @@ endif()
 # Qt stuff
 if (ENABLE_QT)
     if (YUZU_USE_BUNDLED_QT)
-        # Qt 6.8+ is broken on macOS (??)
-        if (APPLE)
-            AddQt(Eden-CI/Qt 6.7.3)
-        else()
-            AddQt(Eden-CI/Qt 6.11.1)
-        endif()
+        AddQt(Eden-CI/Qt 6.11.1)
     else()
         message(STATUS "Using system Qt")
         if (NOT Qt6_DIR)