message: reduce size of HwIndexBuffer
  this limits the index count to 27 bits
diff: @@ -76,12 +76,15 @@ struct HwBufferObject : public HwBase {
  };
  struct HwIndexBuffer : public HwBase {
  - uint32_t count{};
  - uint8_t elementSize{};
  + uint32_t count : 27;
  + uint32_t elementSize : 5;
  - HwIndexBuffer() noexcept = default;
  + HwIndexBuffer() noexcept : count{}, elementSize{} { }
  HwIndexBuffer(uint8_t elementSize, uint32_t indexCount) noexcept :
  count(indexCount), elementSize(elementSize) {
  + // we could almost store elementSize on 4 bits because it's never > 16 and never 0
  + assert_invariant(elementSize > 0 && elementSize <= 16);
  + assert_invariant(indexCount < (1u << 27));
  }
  };
  