Roll SwiftShader from a62e8dbc3467 to 28718d8b4108 (2 revisions)

https://swiftshader.googlesource.com/SwiftShader.git/+log/a62e8dbc3467..28718d8b4108

2023-05-15 bclayton@google.com Update SPIR-V Tools to 51892874b
2023-05-15 bclayton@google.com Update SPIR-V Headers to 268a06176

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/swiftshader-dawn-autoroll
Please CC bajones@google.com,webgpu-developers@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in SwiftShader: https://bugs.chromium.org/p/swiftshader/issues/entry
To file a bug in Dawn: https://bugs.chromium.org/p/dawn/issues/entry

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

Bug: None
Tbr: bajones@google.com
Change-Id: Id58fdcb8339f42267bf57c398b2e370b52737111
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/132929
Commit-Queue: Dawn Autoroller <dawn-autoroll@skia-public.iam.gserviceaccount.com>
Bot-Commit: Dawn Autoroller <dawn-autoroll@skia-public.iam.gserviceaccount.com>

DEPS

@@ -141,7 +141,7 @@ deps = {
   },
 
   'third_party/swiftshader': {
-    'url': '{swiftshader_git}/SwiftShader@a62e8dbc3467471953e0d81192b3ef94e5d40549',
+    'url': '{swiftshader_git}/SwiftShader@28718d8b4108d69d239542ab58f1a3e40c97fbb2',
     'condition': 'dawn_standalone',
   },