- add compile option for mxArrayToString

[fbergmann]

Description

To support older matlab versions, it would be good to be able to switch between the use of
mxArrayToString and mxArrayToUTF8String. This PR adds a configuration option
WITH_MATLAB_UTF8STRING that is on by default.

Motivation and Context

compile on older matlab

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Change in documentation

Checklist:

• I have updated all documentation necessary.
• I have checked spelling in (new) comments.

Testing

• Testing is done automatically and codecov shows test coverage
• This cannot be tested automatically