Give SwitchCase it's own Statement::Kind value

Disambiguates Switch from SwitchCase, and makes is() and as() work.

Change-Id: I9b9b71dabd730247b20ec9b6df02b87e4978d534
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/316577
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/sksl/SkSLDehydrator.cpp b/src/sksl/SkSLDehydrator.cpp
index 0035a21..4f93647 100644
--- a/src/sksl/SkSLDehydrator.cpp
+++ b/src/sksl/SkSLDehydrator.cpp
@@ -473,6 +473,9 @@
                 }
                 break;
             }
+            case Statement::Kind::kSwitchCase:
+                SkASSERT(false);
+                break;
             case Statement::Kind::kVarDeclaration: {
                 const VarDeclaration& v = s->as<VarDeclaration>();
                 this->writeU8(Rehydrator::kVarDeclaration_Command);