Resolve "Linear interpolator only works for minimal shapes and trivial extensions"

What does this MR do?

Fix the linear interpolator algorithm by calling get_knot_indices with the correct argument (coordinates in mesh units pos_unit, not physical units pos). Update the unit test to cover more complicated shapes in the 2D test and non-trivial extensions in the 3D test.

Input data fields now lead to the correct results:

Input data set:

Before (left), after (right):

Is there something that needs to be double checked?

• Ensure the interpolator really works as intended

Can this MR be accepted?

• Implemented fix
• Updated test-interpolators unit test
• Pipeline passing
• Added entry to CHANGELOG.md

Related issues

Closes #154 (closed)