Diagnostics: Use command-line option forms in messages

Tweak how we include the diagnostic category name in diagnostic messages
to use the 'command-line option form' (i.e. lower case with hyphens)
rather than the 'identifier form' (upper case with underscores). This
looks nicer, as it avoids unnecessary 'shouting'.

Source/cmMessenger.cxx

@@ -2,11 +2,10 @@
    file LICENSE.rst or https://cmake.org/licensing for details.  */
 #include "cmMessenger.h"
 
+#include <algorithm>
 #include <sstream>
 #include <utility>
 
-#include <cm/string_view>
-
 #include "cmDocumentationFormatter.h"
 #include "cmMessageMetadata.h"
 #include "cmMessageType.h"
@@ -49,6 +48,14 @@ char const* getMessageTypeStr(MessageType t)
   return "Warning";
 }
 
+std::string getDiagnosticCategoryStr(cmDiagnosticCategory category)
+{
+  std::string out = cmSystemTools::LowerCase(
+    cmDiagnostics::GetCategoryString(category).substr(4));
+  std::replace(out.begin(), out.end(), '_', '-');
+  return out;
+}
+
 cm::StdIo::TermAttr getMessageColor(MessageType t)
 {
   switch (t) {
@@ -250,8 +257,7 @@ void cmMessenger::DisplayMessage(MessageType type,
   // Print the message preamble.
   msg << "CMake " << getMessageTypeStr(type);
   if (category != cmDiagnostics::CMD_NONE) {
-    cm::string_view const cname = cmDiagnostics::GetCategoryString(category);
-    msg << " (" << cname.substr(4) << ')';
+    msg << " (" << getDiagnosticCategoryStr(category) << ')';
   }
 
   // Add the immediate context.