First steps towards ACTS track convertor, together with simple unit test.

This is a first attempt of actually adding the Trk::Track to ACTS track conversion (obviously this does not run in production).

There is some commented out code, because there is missing functionality in MultiTrajectory.icc (see ATLASRECTS-7593). Next steps would be to fix this and add in the uncommented code, and also to try to actually verify that the content is correct.

I have added a basic JSON comparison test, which currently only looks at dparams and positions. This test will always succeed for the moment, since I cannot add a failing test (i.e. it is detecting important differences).

A typical example is:

ERROR: Acts and Trk pos differ for track 47
Acts pos: [14.626742362976074, 8.521271705627441, 2.5258584022521973, 0.24653148651123047, -9.38192081451416, 2.4695992469787598, 0.0, 0.0, 0.0]
Trk pos: [-0.004468011308443883, -0.005196697389204015, -71.36492156982422, -0.004468011308443883, -0.005196697389204015, -71.36492156982422, -25.758201244678443, 21.291873164658153, 672.4, -87.07879583756585, 66.39345841450809, 2359.826]

I think these differences are probably expected, since I cannot currently set a reference surface for the track states.

cc @tbold @pagessin @ncalace @asalzbur