input: deprecate b_dead, b_eof and b_error

Those values are writable by the input thread, and thus inaccessible
to other threads. Any remaining use of those (in VLM, podcast and
interfaces notably) is an undefined memory access, a bug.

include/vlc_input.h

@@ -219,17 +219,16 @@ typedef struct input_resource_t input_resource_t;
 
 /**
  * Main structure representing an input thread. This structure is mostly
- * private. The only public fields are READ-ONLY. You must use the helpers
- * to modify them
+ * private. The only public fields are read-only and constant.
  */
 struct input_thread_t
 {
     VLC_COMMON_MEMBERS
 
-    bool b_error;
-    bool b_eof;
+    bool b_error VLC_DEPRECATED;
+    bool b_eof VLC_DEPRECATED;
     bool b_preparsing;
-    bool b_dead;
+    bool b_dead VLC_DEPRECATED;
 
     /* All other data is input_thread is PRIVATE. You can't access it
      * outside of src/input */