WIP: FindMatlab: Enable control over API in matlab_add_mex
This PR addresses the additional FindMatlab issues raised in #18419 (closed).
- Include the appropriate
*_mexapi_version.*
file in the build under the control of (optional) user specified value MEX_API for Matlab >=2016b - set
MATLAB_DEFAULT_RELEASE=R20XXx
under control of (optional) user specified value DEFAULT_RELEASE for Matlab >=2018a
Follows guidance given at: https://www.mathworks.com/matlabcentral/answers/377799-compiling-mex-files-without-the-mex-command