[spirv] Update SPIRV-Tools and SPIRV-Headers. (#3296)

Picks up more KHR ray tracing changes.

external/SPIRV-Headers

@@ -1 +1 @@
-Subproject commit 104ecc356c1bea4476320faca64440cd1df655a3
+Subproject commit f027d53ded7e230e008d37c8b47ede7cd308e19d

external/SPIRV-Tools

@@ -1 +1 @@
-Subproject commit cd590fa3341284cd6d1ee82366155786cfd44c96
+Subproject commit 21f7c5675da3a45c13024dc1169438eb4e8f7e0c