Add a Bitmap::detachBytes method

This allows us to share bitmap bytes with code that doesn't have a depency on rive_decoders.

Diffs=
58cc49580 Add a Bitmap::detachBytes method (#5763)

Co-authored-by: Chris Dalton <99840794+csmartdalton@users.noreply.github.com>

.rive_head

diff --git a/.rive_head b/.rive_head
index bca50bc..1e13964 100644
--- a/.rive_head
+++ b/.rive_head
@@ -1 +1 @@
-30351d475a956cf0fd13dbe26257e057cc14524f
+58cc495802007c308ee4aa7b27dd755baaff7492

decoders/include/rive/decoders/bitmap_decoder.hpp

diff --git a/decoders/include/rive/decoders/bitmap_decoder.hpp b/decoders/include/rive/decoders/bitmap_decoder.hpp
index 94a69f5..05e295d 100644
--- a/decoders/include/rive/decoders/bitmap_decoder.hpp
+++ b/decoders/include/rive/decoders/bitmap_decoder.hpp
@@ -36,6 +36,7 @@
     uint32_t height() const { return m_Height; }
     PixelFormat pixelFormat() const { return m_PixelFormat; }
     const uint8_t* bytes() const { return m_Bytes.get(); }
+    std::unique_ptr<const uint8_t[]> detachBytes() { return std::move(m_Bytes); }
     size_t byteSize() const;
     size_t byteSize(PixelFormat format) const;
     size_t bytesPerPixel(PixelFormat format) const;