What should we add?

In the spirit of #2788, it would be nice to reduce the leading space currently present inside boxes when drawing a circuit with matplotlib. It seems this could make some circuit drawings significantly shorter.

qc = QuantumCircuit(2)
with qc.box():
    qc.h([0,1])
qc.draw('mpl')
with qc.box():
    qc.x([0,1])
qc.draw('mpl')