Ticket3897 disable mode save

[John-Holt-Tessella]

Description of work

Save incoming beams for all componetns on enter disable mode
Restore on init

To test

ISISComputingGroup/IBEX#3897

Acceptance criteria

See ticket

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Code Review

• Is the code of an acceptable quality?
• Has the author taken into account the multi-threaded nature of the code?
• Have the changes been documented in the release notes. If so, do they describe the changes appropriately?
• Has the manual system tests spreadsheet been updated?

Functional Tests

• Do changes function as described? Add comments below that describe the tests performed.

Final steps

• Reviewer has updated the submodule in the main EPICS repo? See Reviewing work for the subModules of EPICS in the Git workflow page for details.
• Reviewer has moved the release notes entry for this ticket in the "Changes merged into master" section

[aaron-long]

Please try the following:

1. Zero beamline in Polarised NR
2. Enter Disabled mode and change theta to 0.1
3. Restart the REFL IOC
4. Check Theta RBV -> it will state 0.1
5. Move theta to 0.0 -> RBV will instantly update to 0.0

Also:

1. Zero beamline in Polarised NR
2. Enter Disabled mode and change theta to 0.1
3. Restart the REFL IOC
4. Attempt to change alignment for PDangle, PDoffset etc (relating to theta) -> The current position will move as the value for the defined position + some existing offset from the saved beam