CxxUtils: Add normalizeFunctionName.

Move code here from AthenaKernel so that it can be used from analysis releases:

 * @brief Normalize a pretty-printed C++ function name.
 * @param fname The name to normalize.
 *
 * A C++ compiler can provide a complete printable name of the current function,
 * though for example __PRETTY_FUNCTION__.  This is useful to include in
 * diagnostic messages.  However, the exact string generated by different
 * compilers may differ slightly.  This can then cause issues if one is
 * trying to compare the output of tests to an expected reference.
 *
 * This function tries to normalize the function name strings so that they
 * are the same, at least between gcc and clang.