Merge pull request #13773 from drwells/refactor-function-parser

diff --cc include/deal.II/base/function_parser.h
Simple merge

diff --cc include/deal.II/base/mu_parser_internal.h
Simple merge

diff --cc include/deal.II/base/tensor_function_parser.h
Simple merge

diff --cc source/base/CMakeLists.txt
Simple merge

diff --cc source/base/function_parser.cc
Simple merge

diff --cc source/base/mu_parser_internal.cc
Simple merge

diff --cc source/base/tensor_function_parser.cc
Simple merge