Stop ReflectometryReductionOneLiveData from re-writing the spectra map on instrument load

[rbauststfc]

Description of work

Summary of work

Changes the step in ReflectometryReductionOneLiveData that loads the instrument so that it doesn't re-write the spectra map, as this can result in spectra being associated with the wrong detectors.

Fixes #38202.

Further detail of work

The live data workspace already has the instrument loaded, but we need to re-load it because many of the Reflectometry IDFs position their pixels based on the theta value in the log. We add this theta value as part of setting up the workspace in ReflectometryReductionOneLiveData, so we then re-load the instrument to apply the changes. Re-writing the spectra map under these circumstances can lead to spectra being associated with the wrong detector pixels. This PR fixes that issue.

There were a few updates/additions required for the unit tests, and I've also refactored the tests in a couple of places to avoid code duplication.

To test:

1. To prevent the algorithm attempting to look up information from the instrument, edit the code in method _live_value_list, to provide values for _theta_name, _s1vg_name and _s2vg_name:

self._theta_name(): LiveValue(2.3, "deg", self._alternative_theta_name(), LiveValue.LOG_TYPE_NUM_SERIES),
self._s1vg_name(): LiveValue(1.0, "m", self._alternative_s1vg_name(), LiveValue.LOG_TYPE_NUM_SERIES),
self._s2vg_name(): LiveValue(3.0, "m", self._alternative_s2vg_name(), LiveValue.LOG_TYPE_NUM_SERIES),

2. Run the following script:

in_ws = LoadNexus("SURF138942")
out_ws = ReflectometryReductionOneLiveData(InputWorkspace=in_ws, Instrument="SURF")

It should complete successfully. If you check the detector table on in_ws (i.e. using Show Detector from the right click menu) then you should see detectors 20001, 20002, 30001 listed.

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