Add basic reflection query for checking if entry point is "sample-rate"

- This really just checks two basic things:
  1. Was there any global variable declared with `in` and `sample`?
  2. Did any code encountered during lowering referenece `gl_SampleIndex`?

- This doesn't cover what HLSL could need, nor what we would need for cross-compilation. Consider it GLSL-specific for now.

- In order to generate the information with even a reasonable chance of being accurate (not giving a ton of false positives) I tried to integrate the checks into the lowering process (so they only see code that is referenced, one hopes).
  - For this to work with my testing setup, I needed to make sure that lowering is always performed, prior to emitting reflection info
  - This change broke several reflection tests, because they had been using code that wouldn't actually pass the downstream compiler. I checked in fixes for those.

1 files changed, 4 insertions, 2 deletions

diff --git a/tests/reflection/image-types.glsl b/tests/reflection/image-types.glsl
index 21cd2b629..73ecdaa82 100644
--- a/tests/reflection/image-types.glsl
+++ b/tests/reflection/image-types.glsl
@@ -2,9 +2,11 @@
 
 // Confirm that we expose GLSL `image` types through reflection
 
-uniform imageBuffer iBuffer;
+layout(rgba32f)
+uniform writeonly imageBuffer iBuffer;
 
-uniform image2D i2D;
+layout(rgba32f)
+uniform writeonly image2D i2D;
 
 void main()
 {}