Enhance CMake configuration for UI tests and SDL2 linking

- Added support for UI tests in the CMake configuration by introducing the YAZE_ENABLE_UI_TESTS option, ensuring proper linking with the ImGuiTestEngine if available.
- Updated SDL2 linking in test CMakeLists to use variable targets for improved flexibility and compatibility across platforms.
- Modified sprite_position_test to check for ROM file existence using std::ifstream for better error handling.

test/CMakeLists.txt

@@ -72,7 +72,7 @@ target_include_directories(
 
 target_link_libraries(
   extract_vanilla_values
-  SDL2::SDL2
+  ${SDL_TARGETS}
   asar-static
   ${ABSL_TARGETS}
   ${PNG_LIBRARIES}
@@ -97,7 +97,7 @@ target_include_directories(
 
 target_link_libraries(
   yaze_test
-  SDL2::SDL2
+  ${SDL_TARGETS}
   asar-static
   ${ABSL_TARGETS}
   ${PNG_LIBRARIES}