Cleanup: rename BLI_thread.h API

- Use BLI_threadpool_ prefix for (deprecated)
  thread/listbase API.
- Use BLI_thread as prefix for other functions.

See P614 to apply instead of manually resolving conflicts.

source/gameengine/VideoTexture/VideoFFmpeg.cpp

@@ -467,8 +467,8 @@ bool VideoFFmpeg::startCache()
 			CachePacket *packet = new CachePacket();
 			BLI_addtail(&m_packetCacheFree, packet);
 		}
-		BLI_init_threads(&m_thread, cacheThread, 1);
-		BLI_insert_thread(&m_thread, this);
+		BLI_threadpool_init(&m_thread, cacheThread, 1);
+		BLI_threadpool_insert(&m_thread, this);
 		m_cacheStarted = true;
 	}
 	return m_cacheStarted;
@@ -479,7 +479,7 @@ void VideoFFmpeg::stopCache()
 	if (m_cacheStarted)
 	{
 		m_stopThread = true;
-		BLI_end_threads(&m_thread);
+		BLI_threadpool_end(&m_thread);
 		// now delete the cache
 		CacheFrame *frame;
 		CachePacket *packet;