Add Missing MATLAB Function Implementations

[CoolSpy3]

Description This PR adds two MATLAB functions that I discovered were missing as part of #6752 (wbu_system_tmpdir and wbu_system_webots_instance_path). After either one of these two PRs is merged, the other should be updated to remove the explicit exclusions for these functions in the new MATLAB test.

Tasks Add the list of tasks of this PR.

• [x] Update the changelog