mtmd: add mtmd_bitmap_set_mergeable (#27348)

tools/mtmd/mtmd-internal.h

@@ -0,0 +1,19 @@
+#pragma once
+
+#include "mtmd.h"
+
+#include <string>
+#include <vector>
+
+// !!! Internal header, to be used by mtmd and its unit tests only !!!
+
+#define MTMD_INTERNAL_HEADER
+
+// bitmap is null for text parts
+struct mtmd_input_part {
+    std::string text;
+    const mtmd_bitmap * bitmap;
+};
+
+// [QWEN_VIDEO] merged parts are erased from `parts`, so one group always maps to one part
+std::vector<std::vector<const mtmd_bitmap *>> mtmd_group_mergeable_bitmaps(std::vector<mtmd_input_part> & parts, int n_merge);