Automerge: [ADT] Mark StringSwitch Cases with 6+ arguments as deprecated. NFC. (#163405)

Switch to the `.Cases({S0, S1, ...}, Value)` overload instead.

Update existing uses affected by the deprecation and the surrounding
code (for consistency).

This is a part of a larger cleanup of StringSwitch. The goal is to
eventually deprecate all manually-enumerated overloads of Cases with a
hardcoded number of case values (in favor of passing them via an
initializer list). You can find the full explanation here:
llvm/llvm-project#163117.

Start small (6+ arguments) to keep the number of changes manageable.

Author: kuhar

llvm/include/llvm/ADT/StringSwitch.h

@@ -14,6 +14,7 @@
 #define LLVM_ADT_STRINGSWITCH_H
 
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Compiler.h"
 #include "llvm/Support/ErrorHandling.h"
 #include <cassert>
 #include <cstring>
@@ -38,7 +39,7 @@ namespace llvm {
 ///   .Case("green", Green)
 ///   .Case("blue", Blue)
 ///   .Case("indigo", Indigo)
-///   .Cases("violet", "purple", Violet)
+///   .Cases({"violet", "purple"}, Violet)
 ///   .Default(UnknownColor);
 /// \endcode
 template<typename T, typename R = T>
@@ -107,31 +108,36 @@ class StringSwitch {
     return CasesImpl(Value, {S0, S1, S2, S3, S4});
   }
 
+  [[deprecated("Pass cases in std::initializer_list instead")]]
   StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
                       StringLiteral S3, StringLiteral S4, StringLiteral S5,
                       T Value) {
     return CasesImpl(Value, {S0, S1, S2, S3, S4, S5});
   }
 
+  [[deprecated("Pass cases in std::initializer_list instead")]]
   StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
                       StringLiteral S3, StringLiteral S4, StringLiteral S5,
                       StringLiteral S6, T Value) {
     return CasesImpl(Value, {S0, S1, S2, S3, S4, S5, S6});
   }
 
+  [[deprecated("Pass cases in std::initializer_list instead")]]
   StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
                       StringLiteral S3, StringLiteral S4, StringLiteral S5,
                       StringLiteral S6, StringLiteral S7, T Value) {
     return CasesImpl(Value, {S0, S1, S2, S3, S4, S5, S6, S7});
   }
 
+  [[deprecated("Pass cases in std::initializer_list instead")]]
   StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
                       StringLiteral S3, StringLiteral S4, StringLiteral S5,
                       StringLiteral S6, StringLiteral S7, StringLiteral S8,
                       T Value) {
     return CasesImpl(Value, {S0, S1, S2, S3, S4, S5, S6, S7, S8});
   }
 
+  [[deprecated("Pass cases in std::initializer_list instead")]]
   StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
                       StringLiteral S3, StringLiteral S4, StringLiteral S5,
                       StringLiteral S6, StringLiteral S7, StringLiteral S8,