[sil-verifier] Split SILVerifier verificationFailure into separate functions for Instructions, Arguments, and add a variant for Values.

This also required me to change how we handled which instruction/argument we
emit an error about in the verifier. Previously we were using two global
variables that we made nullptr to control which thing we emitted an error about.
This was unnecessary. Instead I added a little helper struct that internally
controls what we will emit an error about and an external "guard" RAII struct
that makes sure we push/pop the instruction/argument we are erroring upon
correctly.

SwiftCompilerSources/Sources/SIL/Utilities/Verifier.swift

@@ -22,7 +22,7 @@ private func require(_ condition: Bool, _ message: @autoclosure () -> String, at
   if !condition {
     let msg = message()
     msg._withBridgedStringRef { stringRef in
-      BridgedVerifier.verifierError(stringRef, atInstruction.bridged, Optional<Argument>.none.bridged)
+      BridgedVerifier.verifierError(stringRef, atInstruction.bridged)
     }
   }
 }