Roll SwiftShader from b7de6caa43b9 to 6cbc24686901 (7 revisions)

https://swiftshader.googlesource.com/SwiftShader.git/+log/b7de6caa43b9..6cbc24686901

2021-09-20 srisser@google.com Set all provoking vertex feature bools
2021-09-20 srisser@google.com Fully support all 16-bit packed texture formats
2021-09-20 capn@google.com Optimize SPIR-V binary cache reuse
2021-09-20 capn@google.com Add optimization state to the optimized SPIR-V binary cache key
2021-09-20 capn@google.com Cache optimized SPIR-V binaries instead of compiled shaders
2021-09-20 capn@google.com Fix use of deleted shader during compute execution
2021-09-20 capn@google.com Refactor SPIR-V binary storage

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/swiftshader-angle-autoroll
Please CC geofflang@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 ANGLE: https://bugs.chromium.org/p/angleproject/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: geofflang@google.com
Change-Id: I7fb69b6fe3c6710f5a3b7510b2c3b0870232aa08
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3172535
Bot-Commit: angle-autoroll <angle-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: angle-autoroll <angle-autoroll@skia-public.iam.gserviceaccount.com>

DEPS

@@ -491,7 +491,7 @@ deps = {
   },
 
   'third_party/SwiftShader': {
-    'url': '{swiftshader_git}/SwiftShader@b7de6caa43b9d92266603071cc28a7dd50850360',
+    'url': '{swiftshader_git}/SwiftShader@6cbc2468690129b65a067805f775db7cda95c2e2',
     'condition': 'not build_with_chromium',
   },