Add new MATLAB functions to syntax highlighting

The original matlab.vim syntax file was written by Fabrice Guy and last
updated in 2009. This commit brings the highlighting up to the latest
MATLAB release at the time of writing (R2022a).

To find the function definitions, I used some Python to parse the MATLAB
documentation reference page. For more details, see here:
MortenStabenau/matlab-vim@b53b12c