message: Fix skinning on Vulkan
diff: namespace filament {
  -constexpr uint32_t ATTRIBUTE_INDEX_COUNT = 5;
  -
  enum VertexAttribute : uint8_t {
  POSITION = 0, // XYZ position (float3)
  TANGENTS = 1, // tangent, bitangent and normal, encoded as a quaternion (float4)
  @@ -49,6 +47,7 @@ namespace BindingPoints {
  static_assert(BindingPoints::PER_MATERIAL_INSTANCE == BindingPoints::COUNT - 1,
  "Dynamically sized sampler buffer must be the last binding point.");
  +constexpr uint32_t ATTRIBUTE_INDEX_COUNT = 7;
  constexpr size_t MAX_ATTRIBUTE_BUFFERS_COUNT = 8; // FIXME: should match Driver::MAX_ATTRIBUTE_BUFFER_COUNT
  // This value is limited by UBO size, ES3.0 only guarantees 16 KiB.
  