Make scrcpy.h independant of other headers

The header scrcpy.h is intended to be the "public" API. It should not
depend on other internal headers.

Therefore, declare all required structs in this header and adapt
internal code.

app/src/util/log.h

@@ -3,13 +3,6 @@
 
 #include <SDL2/SDL_log.h>
 
-enum sc_log_level {
-    SC_LOG_LEVEL_DEBUG,
-    SC_LOG_LEVEL_INFO,
-    SC_LOG_LEVEL_WARN,
-    SC_LOG_LEVEL_ERROR,
-};
-
 #define LOGV(...) SDL_LogVerbose(SDL_LOG_CATEGORY_APPLICATION, __VA_ARGS__)
 #define LOGD(...) SDL_LogDebug(SDL_LOG_CATEGORY_APPLICATION, __VA_ARGS__)
 #define LOGI(...) SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION, __VA_ARGS__)