Energy Changes: Calculate the bragg angle ourselves

[DominicOram]

From #277 we found that the bragg angle on the DCM BL03I-MO-DCM-01:BRAGG does not update quickly after we set BL03I-MO-DCM-01:ENERGY. We need the bragg angle for lookup tables on movements that we should be able to do at the same time as the energy change and so we will need to work out what the bragg angle is ourselves.

This can be calculated by substituting the d-spacing of Si into bragg's law.

Acceptance Criteria

• We calculate the bragg angle of the DCM early when changing energy
• We move the other motors we have to move at the same time as the DCM energy motor

[DominicOram]

We can read the d-spacing of the DC from BL03I-MO-DCM-01:DSPACING:RBV

[DominicOram]

The metadata from DiamondLightSource/dodal#722 might also be helpful

[rtuck99]

Paused waiting on DiamondLightSource/dodal#843