Use 16-bit indices for nk_buffer element buffer?

Hello, the library I'm using (bgfx)'s transient buffer element buffer doesn't support 32 bit indices, I could just write data conv to 32 to 16 bit but I'm wondering if there's a way to make it use 16-bit indices instead, don't see anything in `nk_convert_config` or anything.

Thank you!

Start by tracing the nk_convert_config API and the element-buffer data produced by nk_convert, then compare its index format with bgfx's transient buffer requirements. Confirm whether the existing conversion path exposes a suitable 16-bit option and define completion as a supported way to produce 16-bit element indices without requiring callers to convert the data themselves.

Written by the indexing model from the issue text.