zink: limited uniform buffer size so the limits is not exceeded.

See merge request !7

Some implementations don't support the lineWidth-feature, so let's
avoid setting invalid state to them. But since we don't have a fallback
for this, inform the user.

Duncan Hopkins authored Jul 11, 2019 and Erik Faye-Lund committed Sep 13, 2019

The driver can report a minimum alignment for UBOs, and that can be
larger than 64, which we've currently been using. Let's play ball, and
use the reported value instead.

Duncan Hopkins authored Jul 10, 2019 and Erik Faye-Lund committed Sep 13, 2019

There's two things that goes wrong in this code on some drivers:
1. Rounding off the line-width to granularity can push it outside the
   legal range.
2. A granularity of 0.0 results in NaN, because we divide by zero.

So let's make this code a bit more robust.

We need to actually be able to store 8 here, which needs the fourth bit.
We can't reuse the zero-value, because we can do depth-stencil-only
rendering, for instance.

This fixes Quake3, and is more in line with directx semantics.

This gets rid of the nasty location-allocation hack.

We're now adding interface-types during code-emitting, so we need to
defer emitting the entry-point. No biggie, spirv_builder is prepares for
this.

This is the only call-site that wants to specify unique values per
component for any of the get_*_constant functions. So let's give this
its own implementation instead, so we can ease the burden for the rest.

While we're at it, let's move emit_float_const to the same location as
this needs to be defined at.

This is going to make it easier to verify that 1-bit float sizes don't
leak into the rest of the code.