[tests] FIX all tests using MechanicalObject + Reactivate Sofa.Components

[guparan]

When Sofa.Components was activated, its test (bindings/Sofa/tests/Components/Components.py) was the first test executed.
This test contains a root.addObject('RequiredPlugin', name='SofaBaseMechanics').
Well, there is no Python environment cleaning between each test.
Thus SP3 tests benefit from the RequiredPlugin done by all the tests executed before.
That is why the deactivation of Sofa.Components made all those tests fail with "cannot create MechanicalObject".

What I did:

• re-enable Sofa.Components (and its test) and move the test to be the last executed
• fix all SP3 tests that use MechanicalObject with some "RequiredPlugin SofaBaseMechanics"

[jnbrunet]

Thanks a lot @guparan ! This will get our CI back and running 👍