Prevent idle priority threads from potentially starving the FreeRTOS idle task (#3909)

* FuriThread: Make FuriThreadPriorityIdle equal to the FreeRTOS one, remove FuriThreadPriorityNone
  This magic constant was meaningless,
  FuriThreadPriorityNormal is now assigned by default instead.
* Make furi_thread_list_process private
  Its 'runtime' parameter is to be obtained from FreeRTOS,
  which means apps cannot do it.
* DirectDraw: Remove an useless include and fix memory leak
  Makes this debug app compileable with uFBT out of the box

Co-authored-by: あく <alleteam@gmail.com>

applications/debug/direct_draw/direct_draw.c

@@ -1,6 +1,5 @@
 #include <furi.h>
 #include <gui/gui.h>
-#include <gui/canvas_i.h>
 #include <input/input.h>
 
 #define BUFFER_SIZE (32U)
@@ -42,10 +41,11 @@ static DirectDraw* direct_draw_alloc(void) {
 static void direct_draw_free(DirectDraw* instance) {
     furi_pubsub_unsubscribe(instance->input, instance->input_subscription);
 
-    instance->canvas = NULL;
     gui_direct_draw_release(instance->gui);
     furi_record_close(RECORD_GUI);
     furi_record_close(RECORD_INPUT_EVENTS);
+
+    free(instance);
 }
 
 static void direct_draw_block(Canvas* canvas, uint32_t size, uint32_t counter) {