Expose bitDepth to MediaMetadataRetriever

Bug: b/217378477
Test:
Change-Id: I16dabdf9aaabf341a9cebb1624e464155196a5a8
diff --git a/media/libheif/HeifDecoderImpl.h b/media/libheif/HeifDecoderImpl.h
index 2b9c710..86a8628 100644
--- a/media/libheif/HeifDecoderImpl.h
+++ b/media/libheif/HeifDecoderImpl.h
@@ -54,6 +54,8 @@
 
     size_t skipScanlines(size_t count) override;
 
+    uint32_t getColorDepth() override;
+
 private:
     struct DecodeThread;