message: Update RELEASE_NOTES for 1.9.20
diff: @@ -5,8 +5,22 @@ A new header is inserted each time a *tag* is created.
  ## Next release (main branch)
  +## v1.9.21
  +
  ## v1.9.20
  +Android: Fix VSM.
  +engine: Introduce BufferObject API.
  +engine: Add new isTextureSwizzleSupported API on Texture.
  +engine: Add support to Metal and Vulkan backends for texture swizzling.
  +engine: Add new DoF settings (native/half res, gather kernel ring counts, CoC radius clamp).
  +engine: DoF quality and performance improvements.
  +engine: Fix high-quality upsampling issue with SSAO.
  +Java: Expose `TransformManager.getParent(int)`.
  +samples: Add Metal and Vulkan backend support to Suzanne sample.
  +WebGL: expose fitIntoUnitCube to JS.
  +WebGL: support for multiple <canvas> elements.
  +
  ## v1.9.19
  - engine: Fix Metal bug when setGeometryAt is called multiple times.
  