Turned on preserve bindings to impellerc (#167203)

fixes https://github.com/flutter/flutter/issues/116900

## Pre-launch Checklist

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there for submitting PRs.
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- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
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- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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engine/src/flutter/impeller/compiler/spirv_compiler.cc

diff --git a/engine/src/flutter/impeller/compiler/spirv_compiler.cc b/engine/src/flutter/impeller/compiler/spirv_compiler.cc
index 9e0f66f..5861853 100644
--- a/engine/src/flutter/impeller/compiler/spirv_compiler.cc
+++ b/engine/src/flutter/impeller/compiler/spirv_compiler.cc
@@ -282,6 +282,7 @@
 
   options.SetAutoBindUniforms(true);
   options.SetAutoMapLocations(true);
+  options.SetPreserveBindings(true);
 
   options.SetOptimizationLevel(optimization_level);
 

engine/src/flutter/impeller/fixtures/BUILD.gn

diff --git a/engine/src/flutter/impeller/fixtures/BUILD.gn b/engine/src/flutter/impeller/fixtures/BUILD.gn
index f4e6bc5..d42088e 100644
--- a/engine/src/flutter/impeller/fixtures/BUILD.gn
+++ b/engine/src/flutter/impeller/fixtures/BUILD.gn
@@ -68,6 +68,10 @@
     "texture.vert",
   ]
 
+  if (impeller_enable_vulkan) {
+    vulkan_exclusions = [ "half.frag" ]
+  }
+
   if (impeller_enable_opengles) {
     gles_exclusions = [
       "sample.comp",

engine/src/flutter/impeller/tools/shaders.gni

diff --git a/engine/src/flutter/impeller/tools/shaders.gni b/engine/src/flutter/impeller/tools/shaders.gni
index 140b886..cfa2099 100644
--- a/engine/src/flutter/impeller/tools/shaders.gni
+++ b/engine/src/flutter/impeller/tools/shaders.gni
@@ -140,7 +140,11 @@
       if (defined(invoker.vulkan_language_version)) {
         vulkan_language_version = invoker.vulkan_language_version
       }
-      shaders = invoker.shaders
+      if (defined(invoker.vulkan_exclusions)) {
+        shaders = invoker.shaders - invoker.vulkan_exclusions
+      } else {
+        shaders = invoker.shaders
+      }
       analyze = analyze
     }
   }