GetCppName: Mangled version of the C++ symbol

[couet]

Explain what you would like to see improved and how.

The function TMetaUtils::GetCppName returns a mangled version of the C++ symbol that can be used in C++ as a variable name. It replaces in a string all the characters that are invalid in a C++ variable name by some mangled version. The core of the code is this switch:

      switch(c) {
         case '+': repl = "pL"; break;
         case '-': repl = "mI"; break;
         case '*': repl = "mU"; break;
         case '/': repl = "dI"; break;
         case '&': repl = "aN"; break;
         case '%': repl = "pE"; break;
         case '|': repl = "oR"; break;
         case '^': repl = "hA"; break;
         case '>': repl = "gR"; break;
         case '<': repl = "lE"; break;
         case '=': repl = "eQ"; break;
         case '~': repl = "wA"; break;
         case '.': repl = "dO"; break;
         case '(': repl = "oP"; break;
         case ')': repl = "cP"; break;
         case '[': repl = "oB"; break;
         case ']': repl = "cB"; break;
         case '!': repl = "nO"; break;
         case ',': repl = "cO"; break;
         case '$': repl = "dA"; break;
         case ' ': repl = "sP"; break;
         case ':': repl = "cL"; break;
         case '"': repl = "dQ"; break;
         case '@': repl = "aT"; break;
         case '\'': repl = "sQ"; break;
         case '\\': repl = "fI"; break;
      }

Seems to me a few characters are missing in that switch ie: # ? {} ` ; I found this while working on this PR: https://github.com/root-project/root/pull/15377#pullrequestreview-2029558913

Sorry if I am wrong.