GUI: Change the number of significant figures displayed for blocks easily

[KathrynBaker]

As someone using IBEX, I want to be able to change the number of significant figures I'm showing in a block easily

Acceptance Criteria

• [ ] There is an option in block creation to set significant figures
• [ ] There is an option in the IOC settings to set significant figures

Notes

This should generally be possible by setting the appropriate field in the record, but a less "privileged knowledge" way of achieving it would be helpful to the instrument scientists

[Tom-Willemsen]

This was discussed briefly in the office as @boeuf-codes was going to pick this up as a training ticket. I don't think it's a training ticket in it's current form.

This could be approached in one of two ways; it's not immediately clear to me which way is better (and from a quick discussion with those in the office, it's also not completely obvious to the rest of the team either).

• Option 1: Provide a more user-friendly (but ultimately functionally equivalent) way of setting .PREC on a record, compared to PV sets
  • Setting .PREC is the standard EPICS approach for controlling display precision
  • The mapping between blocks and IOCs is unclear so this would need some thought as to best implementation
  • e.g. blocks coming from other machines/accelerator
  • e.g. MOT:MTR0101 - which IOC does this come from?
• Option 2: Allow the option of overriding precision for blocks (so ignoring .PREC if this flag is set)
  • Implementation looks something like:
  • Extend blocks XML schema to allow this extra tag
  • Pass through the relevant parts of blockserver and GUI code
  • In GU add a new channel type in /uk.ac.stfc.isis.ibex.epics/src/uk/ac/stfc/isis/ibex/epics/pv/Channels.java and uk.ac.stfc.isis.ibex.instrument.channels for values with fixed precision
  • In setDisplayBlocks (/uk.ac.stfc.isis.ibex.configserver/src/uk/ac/stfc/isis/ibex/configserver/displaying/DisplayConfiguration.java) GUI needs to choose whether to use the new channel type or the existing channel type based on the new metadata tag
  • This moves away from standard EPICS display-control mechanisms which I'm not sure is the right approach. I think we should stay as close as we can to standards in case we decide to move blocks to a different display solution later on.
• Maybe other options I've not considered.

Most of this discussion would also equivalently apply to https://github.com/ISISComputingGroup/IBEX/issues/7154

Before picking up/pointing this ticket we should decide which appraoch we're taking.