Give them explicit size information and make them unsigned where it
matters. This solves an issue where platforms setting one or more of
these limits as UINT32_MAX would end up overflowing to (-1) due to the
representation as `int`.

Now the valid value range is a more explicit part of the API semantics,
with GPU implementations being required to convert and clamp as needed.

As an aside, also log the missing field max_buffer_texels.