Unit stride access of blocked Coefficients

Running some benchmarks with @jhale we've noticed that there was a performance regression introduced in https://github.com/FEniCS/ffcx/pull/645.

More specifically, before the above PR any blocked Coeffcient (e.g. a vector-valued material property) would be first copied into a temporary outside of the quadrature loop such that in the hot loop it is accessed with unit stride, see removed logic https://github.com/FEniCS/ffcx/pull/645

For higher order quadrature rules (but otherwise simple scalar trees) this could lead to >30% performance regression.