Add missing include file to StringExtrasTest.cpp

Use of std::isupper and std::islower need <cctype> header file. Fix
that and also fix the header of a file to match the file name.

PiperOrigin-RevId: 260816852

mlir/include/mlir/Support/StringExtras.h

@@ -24,6 +24,8 @@
 
 #include "llvm/ADT/StringExtras.h"
 
+#include <cctype>
+
 namespace mlir {
 /// Converts a string to snake-case from camel-case by replacing all uppercase
 /// letters with '_' followed by the letter in lowercase, except if the

mlir/unittests/IR/StringExtrasTest.cpp

@@ -1,4 +1,4 @@
-//===- StringExtras.cpp - Tests for utility methods in StringExtras.h -----===//
+//===- StringExtrasTest.cpp - Tests for utility methods in StringExtras.h -===//
 //
 // Copyright 2019 The MLIR Authors.
 //