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, 3 insertions, 3 deletions

diff --git a/tests/reflection/multi-file.hlsl.expected b/tests/reflection/multi-file.hlsl.expected
index 3dc23c11c..4ad95fb35 100644
--- a/tests/reflection/multi-file.hlsl.expected
+++ b/tests/reflection/multi-file.hlsl.expected
@@ -236,12 +236,12 @@ standard output = {
     ],
     "entryPoints": [
         {
-            "name": "main",
+            "name": "mainFS",
             "stage:": "fragment"
         },
         {
-            "name": "main",
-            "stage:": "fragment"
+            "name": "mainVS",
+            "stage:": "vertex"
         }
     ]
 }