move snapshots to beginning of file

this way we can stream out the snapshots every time
we GC and then free their memory, then later just finish
it up with the string heap, types, and static frames.

src/profiler/heapsnapshot.c

@@ -1042,12 +1042,12 @@ void collection_to_filehandle(MVMThreadContext *tc, MVMHeapSnapshotCollection *c
     HeapDumpIndex index = {0};
     fputs("MoarHeapDumpv002", fh);
 
+    snapshots_to_filehandle(tc, col, fh, &index);
+
     string_heap_to_filehandle(tc, col, fh, &index);
     types_to_filehandle(tc, col, fh, &index);
     static_frames_to_filehandle(tc, col, fh, &index);
 
-    snapshots_to_filehandle(tc, col, fh, &index);
-
     index_to_filehandle(tc, col, fh, &index);
 
     MVM_free(index.snapshot_sizes);