Incorrect parameter order for encode and decode special character functions

[zachcran]

Describe the bug
According to the CMakePPLang documentation, return parameters should come before input parameters. cpp_encode_special_chars and cpp_decode_special_chars have this in the opposite order and should be fixed.

Additional context
This is also going to require fixing the calls to cpp_encode_special_chars in:

• cmake/cmakepp_lang/class/detail_/class.cmake.in and
• cmake/cmakepp_lang/utilities/call_fxn.cmake,

along with calls to cpp_decode_special_chars in:

• cmake/cmakepp_lang/utilities/call_fxn.cmake.